If I might offer you a bit of advice...
Return the dirty dingleberry sliders if you are 2wd and get some of the Tejas Speed Engineering motor mounts. In effect you will skip needing the trans mount (so return it too or sell it) and use your stock crossmember and just need to slide it up or down depending on a few things (like engine placement, if you are 2 or 4wd, etc etc). The motor will be further forward and lifted up some so you wont have to notch your front cross member to clear the oil pan and then with a 4l8_ on 2wd I have been informed that everything lined up on the crossmembers if you are 2wd, so you won't have to do too much but you still want to get a good aluminum drive shaft regardless because as speeds approach 100+ on dynos they have been known to fail and break, and many dyno guys are not allowing dyno tuning if they are smart enough to know you are running an original SB driveshaft. If you are 4wd the same applies but you don't need a monster front driveshaft for daily driving so just plan on building bigger if you are going to the mud races and what not, but at that point you better start looking for a dana 60 because you'll be breaking 10 bolt front axles before a built driveshaft breaks.
You can use the fans and radiator from the yukon but fitting it into the square you might need a electric fan shroud to fit better. Tejas can help you there too and also provide a PCM mount for a fender mounted PCM in pretty much the OEM location as the stock harness allows for (On the drivers fender well)
Headers you can pretty much go with Speed Engineering LS swap Truck headers. They have a new model with a v band clamp on it so you can really setup a nice OEM style exhaust. Skip cut outs, those are for drag racers or people who do not care about hearing loss. There will be about a 5 week lead time, but honestly they are worth the wait, Likewise there have been some white box hooker headers on ebay (not sure on sellers) and they are real hooker swap headers and using them will allow you to cobble a system together using a myriad of stock parts if you wish, but to me the ease of the vband clamps (and no gaskets for them) has greater appeal. I'll be doing a 2 into 1 stockish setup on mine using V band clamps to assemble a 2.5 inch Y pipe that funnels into a 3 inch with a flex connector, so it can be removed without taking off everything (for easy transmission access because I am sure I'll blow up my 4l60 sooner (as opposed to later)).
If your donor Fan is a mechanical fan then you can use the square shroud, and the motor being slid up will actually benefit put it right in the spot it needs to be (if you are still using truck accessory brackets..
If you get to noting your donor Rad is crappy (old) you can replace it for about 110 bucks off Amazon and just google CU730 and that is the oem replacement and will bolt right in your truck with use of the big block top radiator hold down plate (I think you can only get them new off LMC)....
The 87 fuel tank will require your sending unit be a TBI sending unit to mount the FI pump as well, just fyi, and its not cheap exactly. Mine was around 80 bucks new.
Make sure and get your fuel pump from a reputable dealer because chinese fakery is rampant on "walbroke" fuel pumps and is not ideal do drop a truck tank (blazer tanks are easy, especially when you put a access hatch in the floor), but it all sucks when the tank is full of fuel. Check here-
http://www.fuel-pumps.net/ They are known to be authorized reseller and know the difference between chinese knockoffs, so can help you identify them.
If your current LS intake has a regulator on the fuel rail don't waste time on the vette regulator. Just get the fuel filter for your year donor truck. That setup is PWM controlled from the ECU and can cause pressure issues if not setup properly. People will tell you they did it with no problem, those same people will also ask questions about why their truck runs like ass when they go WOT.... So rule of thumb is use what your intake fuel rail dictates. It might require you using some additional fuel line for a return line but that's easy and it doesn't have to be fancy stainless finish. Just use Ethanol and FI approved line with FI clamps and you can run a return back to the sending unit really easy.
As far as the harness and PCM goes, either do it yourself on the harness, or spend the money up front and have it done right by someone that isn't a hack and does it for a real business, and not some side hustle. I'm not going to name names but mine was done by one of the worst, and what I got back, he should be ashamed to say he worked on. Essentially I am going to buy another complete harness to have features added back in (which I asked to have) and also so it comes back looking like I expected
The best work and results I have seen is from LSX specialties.
https://www.facebook.com/LSXspecialties/ It is pricy, but it is the finest results. He builds your harness on a board, and when you see it come back, it is a work of art.... Nice braided looming and everything fits because it's been test fit in an engine compartment.
He also does VATS removal and tuning, but the thing to know about tuning is that what you essentially do is put a base tune on your PCM , and the idea is you get your truck together, can get it fired up and running, then tweak and install your exhaust, then do a little self gratification and burnout (because the child inside us demands it) but after that you want to go to a dyno setup and get it dialed in well. The benefit of this is it takes advantage of the EFI swap and proivides you the ability to get the best economy when you are not flogging it, and it will not burn up your motor when you are. The base tune usually runs a nice fat fuel curve that will in no way be "Fuel Efficient" so if you find someone who can do it cheap, go ahead, and let them know your transmission, things you want to keep, and tire and gear sets. After that you might still end up needing to trailer it to a dyno tuner but it just depends on all of the variables sometimes that get overlooked. I think I would Trust LSX to be able to diagnose from afar and hot swap your PCM (meaning get it back to you in a day or two) and usually a decent tuner will make changes and updates for no additional charge.
As far as Dakota Digital gauges go, if you're talking about that digital monstrosity that is all LCD looking, I would honestly save your money and get the gauges that are Analog looking. The digital looking ones have problems where digits start turning into numbers they are not or just going blank because the cold solders come undone, and to be honest I have never heard of someone not having some kind of issues with them. If what you want is something that will be fed by the PCM, then you are better off getting a gauge cluster out of a 91 Blazer or Burb, which uses a VSS signal for your speedo direct from the PCM, and you can even hook up the diagnostic light to run off the dash Check Engine light). You can find them for between 80 to 120 USD, and honestly, it just works. You have to do some pinswaps on your cluster harness, but there is a guide for that too.
One other thing you want to either make sure is added to your harness, or you get and add yourself, os the OBD2 diagnostic port. It essentially consists of 4 wires and the harness builder can leave them as pig tails, at which point you can yank one off a wrecked vehicle or buy a new one and run the wires through your firewall and mount in a convenient place under the dash. You'll need it for tuning, testing, and checking codes when the arise.
Sorry for the book, but I just want to make sure you ask a ton of questions before spending more money on things that end up not working or costing more money. Trust me, I have been through the wringer....
Once you get down the road a little futher and get it running you can start doing things like... Setup cruise control...
Also, are you planning on keeping the AC? The Tejas motor mounts will allow you to keep the AC pump in the stock lower locationi and with some adapter pieces from (I think) coldhose.com you can get the LS AC compressor working with your square body AC if you have all the parts. You can probably replace the necessary stuff for cheap and then get it running with the conversion stuff pretty easy as well... Food for thought.
