I'm doing the swap right now. Read the link Hawk gave and it will give you the details.
You'll need to figure out accessories if you're not getting an f-body LS1 donor.
Also think about:
exhaust (make one or buy stainless woks headers/y-pipe)
motor mounts (buy adapters)
trans mount (make or buy if T56)
speedometer drive (depends on your car - do you need mechanical drive?)
fuel supply & regulator (will need pump upgrade, regulator near engine or LS tank & pump)
I'm also making my own harness. Here's a link for wiring if using the 0411 pcm: http://www.thirdgen.org/forums/ltx-lsx/ ... -into.html
LQ4/T56/3.50 8.8 (next step..TC76)
Build thread: http://ls1tech.com/forums/conversions-hybrids/1819001-1986-iroc-turbo-lq4-t56-build-ac.html
Formerly 95 LT1 [LE2.2]/T56/4.11 9 Bolt..12.6@114MPH