Some basics for the switch to EFI...
Fuel:
You’ll need an EFI fuel tank/fuel cell, or alter your tank to accommodate. With the fleetside trucks most people swap the tank for 1987 truck tanks and sending units, not sure if this applies to the stepside trucks or not. The '87 tanks are baffled and the sending units are designed for in tank pumps, the EFI pumps fit in place of the low pressure pumps originally fitted in the '87.
Sending unit with in tank pump and return line.
EFI rated Fuel pump (58 PSI IIRC)
You’ll need to plumb the fuel feed and return lines with EFI rated line.
You'll need to plumb the feed line with an EFI rated fuel filter
Wire the pump from a relay triggered by the PCM.
It seems like most of the LS stuff has the fuel line on the drivers side near the firewall so make a solid plan to route the fuel lines to that location.
If you have dual tanks it gets significantly more complex, you would also need a 6-port pollack tank valve, the tank selector switch from a 1987 truck, make the wiring harness for pumps and fuel level sender, and additional plumbing.
Wiring:
You’ll need to cut down your LS harness to only what is needed or have a harness made.
You need a PCM, I assume you have one with your harness.
PCM will need to be flashed to remove VATS, and possibly any of the emissions equipment you don't intend to run.
PCM will need to be supplied with 12v constant power, 12v Run/Crank power, and ground
The existing truck wiring doesn’t need to change much except the LS will have all of its own sensors and sending units that communicate with the PCM so you’ll need to run an additional oil pressure and temp sender to your dash gauges.
The LS PCM will not run your speedometer, I’m not sure what your options are on a 2WD to keep the mechanical speedometer or you can switch to an electronic gauge set like Dakota Digital. I suppose it may be possible to add a mechanical speedo gear to the tail housing on a 2WD 4l60 but I cant say for sure.
Physical changes:
One of the other guys can probably chime in on which motor mounts are best.
You will need to relocate the transmission crossmember further back on the frame to accommodate the 4L60. Once the front motor mounts are figured out with the rear of the block close to the firewall, ideally you should be able to mount the crossmember to the transmission and use it as a guide to drill new holes in the frame.
You will need to source a drive shaft from a 2WD 700R4 equipped truck or take yours into a driveline shop to be shortened, your slip yoke from the TH350 should fit the 4L60.
The gear selector input on some of the 4l60E's sticks further off the side of the transmission, you will need to alter (shorten) the Z bar that connects the trans to the frame or replace the gear selector with one from a non "E" 4L60 or 700R4.
You will need to weld in an O2 sensor bung in each exhaust below the manifold
