Note, I've never done an EFI swap into an early pickup. I went another route for EFI.
The toyota harness isn't known for being simple or easy to work on. There's a vendor on pirate that sells a "painless" harness - basically they cut out all of the extra stuff from a factory harness, but the price is high - around $450.

You are going to need decent wiring diagrams.
I'd probably try to put the late model motor in complete with the wiring harness. It's going to have a different distributor, a different ignitor, a diagnostic port, heated 02, EFI relays and a bunch of fun stuff. Figure out what connections are left over and what they do - you really only need to power the EFI system up appropriately, connections to sensors, TPS, 02, ignition, power the fuel pump, and be able to hit the starter to make it run.

If you need help with ECU functions, send me a PM - I can probably help you. I probably can't tell you much about the harness, but the ECU I know pretty well.

Side note:
Toyota did choose low and high impedance injectors across the years. You can't swap injectors, but from the ECU perspective - they're both high impedance setups - the early 22REs have a resistor box in line with the injectors.