I'm in the middle of dropping a 95' 4.3 in my 89' Toy and it all adds up.
You can thin the factory harness if you are decent with wiring and have the time or buy an aftermarket harness. Alot of people Like Jims performance but I had a hard time getting a hold of him so I went with a howell harness. Affordable Fuel injection and Painless Performance both sell harnesses as well.
You will need to figure out the drivetrain as that adds up quick for adapters. I did a TH350 adapted to Toy 21spl cases. Alot of dicking around but not really anything difficult. There is a FAQ thread on PBB and YotaTech has some good build threads.
Good luck!:beer: