Most installs on this level are done by shops full of people who know just wtf they are doing.. Doing it yourself and youre bound to come across alot of issues. As for the harness from a junkyard, its not that simple. You need a harness converted to be used in that chassis with that motor. Invest in one pre-made and youre looking at another 3-400$. You also need an exhaust manifold (as i believe the stock doesnt work in these chassis, atleast it doesnt in an EG), axels, shift linkage, and ecu for that motor. On top of possibly fabricating here and there.
Dont get me wrong, im not trying to rain on your parade and discourage you, but you need to be ready for a long process that eventually may end in rejoice and satiafaction, or utter failure.
I know shops in my area will do a full k swap for 7k, thats parts and labor.