Looking for advice swapping 5.3 and 6L80e into 79k20

Hey yall, new to engine swapping, but interested in fuel injection system in my 79k20. I have a complete donor truck, 2010 Silverado with 5.3 and 6L80e tranny. Just wondering what I can expect to see trying to get this all to work. What kind of mounts will I need for this new trans, and any suggestions of new shifting system to work with the trans? Looking at a Holley terminator system, but not opposed to the original ecu style either. Any advice would be great.

Not worried so much about dropping in the engine itself, but trying to match the new trans with the old transfer case is concerning me. I believe it would be a np203. Any tips would be appreciated thanks!

If you have never done this kind of thing before, then it might be somewhat challenging.
Your talking about a lot of customization, modification, improvisation, fabrication, materba... well maybe not that last one..
But it will require patience and dedication to complete. Don't start the project unless you intend to complete it.

Is the donor 6L80 a 4wd unit as well?
I'm not certain, but I believe if the 6L80 has an NP series T Case on it, a round pattern NP case from earlier years will bolt up. If you have the 203, I believe that's a figure 8 case, and won't bolt directly up, although I'm sure there is a way to adapt it. There are also 27 and 32 spline considerations, your K20 probably has a TH400 and 32 spline? I believe the 6L80 is also 32 spline, but verify all of that. It may be easier to get a later model (~85 and up) round pattern case 205 or 208 (or 241) instead. The later 241 case is rare but may be beneficial as it has a VSS. Some transmissions need that, others don't, I honestly don't know on the 6 speed and it may depend on your engine control choice.

I'm a fan of the GM ECM, but everyone can make their own opinion on that. This isn't uncharted territory, there may not be identical build threads to your setup, but there is information out there that should be able to answer any questions that come up.

It will be time consuming and cost more than you expect but very rewarding. I would forget the 203 and find something more modern. Leaving it in the drivetrain would be like having a supermodel with a snaggle tooth. I would also forget the aftermarket ECU and use the factory unit. There are lots of companies that will modify or provide custom harness's for you. Plug and play.

Motor mounts I suggest the ORD engine crossmember/motor mount combo.
The Holley Terminator is compatible with the six speed, no issue there.
Walters speed and engineering has a VSS kit that replaces the cable drive on the 208/241 xfer cases. Fairly easy install.
Whatever your budget is, double it. The smaller nickel and dimes stuff adds up quickly.
I don’t have any experience with the six speeds, but I believe they are a bit longer and may require you to move the trans crossmember to the rear a bit. This will most likely require lengthening the driveshafts.

6l80e to np203 adapter:

Also might want to do the 'burb tank conversion under the bed unless you need a spare tire. I went with '88 I believe and fitted the pump to the sender.

Save money and build your own AN hoses. I used PAC-625 from Advance Auto for the hard line between engine and tank Areas. Good reviews back then and no issues now. $55 for 50 foot.

Lastly and most important to me with the engine you have, look into AFM/DOD delete. Yes it's about $800 but I would do it if one was going into my truck. No I'm not rich, but one of those would not go into my truck w/o it being hardware deleted.

[edit] see next post and link I posted below.

Camar068 said:

Lastly, look into AFM/DOD delete. Yes it's about $800 but I would do it if one was going into my truck. No I'm not rich, but one of those would not go into my truck w/o it being hardware deleted.

Click to expand...

Coming out of a 2010 I don’t think this will be an issue.

OP, the adapter above for your transfer case and a Tejas steelworks crossmember is the way. The front driveshaft may work but you will probably have to cut or find a right length rear. My last swap I just put the measurement from joint to joint into the eBay search and one from a modern truck popped up at a fraction of having one made.


For the fuel system just spend the money on a Boyd’s. You can go burb or blazer with an in tank sender also but the Boyd’s is a nicer end product.

Transfer case look for a 89-90/91 burb/blazer unit. I used one from a 89 burb and converted the rear to a speed sensor.

kkgp81 said:

Coming out of a 2010 I don’t think this will be an issue.

OP, the adapter above for your transfer case and a Tejas steelworks crossmember is the way. The front driveshaft may work but you will probably have to cut or find a right length rear. My last swap I just put the measurement from joint to joint into the eBay search and one from a modern truck popped up at a fraction of having one made.


For the fuel system just spend the money on a Boyd’s. You can go burb or blazer with an in tank sender also but the Boyd’s is a nicer end product.

Click to expand...

Thanks for putting me on the spot. Made me read up on it again. Lots of info on AFM/DOD below. Thanks again KKG. I've got a different opinion now.

AFM/DOD delete or not

I was thinking 2013ish for AFM/DOD but I’ll chew crow on that.

kkgp81 said:

I was thinking 2013ish for AFM/DOD but I’ll chew crow on that.

Click to expand...

either way, my impression was if it had it, delete/disable it period. Looks like I was was wrong. Plenty of opinions and such on the link I posted.

Thx again

Cduneman, I am currently doing a 5.3 and 4l60 swap in a 86 C20. Alot of work to be done. I stumbled across a YouTube channel I think would help with some of your questions. Ugly Truck Experience. Jerry is great and actually shows how he does what he does. Check em out. Good luck.

Do the AFM/DOD delete, keep the VVT. You will absolutely want to get that 6L80 reworked also... or it will eat itself after ~160k miles. Most of it can be bolted in quick and easy by just pulling the bellhousing and the valve body. Transgo Tow&pro kit, billet 1/2/3/4 piston, and an aftermarket converter with billet front are MUST HAVE for a 6l80. I would personally keep the factory PCM and buy an HP Tuners or EFILive device. Do your own tuning and adjustments. You'll spend $2k for a Holley ECM that will do a worst job of controlling the engine/trans and then still have to pay someone else to tune it or do it yourself anyways.