99 Tahoe motor in 97 blazer?
 

my buddy totaled his Tahoe to day but the entire front end is perfect. He just put 3 grand into his motor and trans and now has no use for it. The motors ( 4.3 and 5.7 vortecs) are VERY similar so wouldn't i just be able to swap the engine harness and drop it in? E-fans? obviously custom exhaust and stuff but either way i don't wanna see his good engine go to waste.

This is one of the easier swaps into a 2nd gen S-series. I would actually add the necessary wiring instead of swapping over harnesses.

ok i thought it should be somewhat easy. What wiring would need to be added? The 2 extra injectors? other than that we have the same sensors at a glance? If he wants to buy a blown up blazer can it be any 2nd gen (95-05)?

Any 96+ yes.