New 4.3 in 87 blazer

i bought this truck with a newer 4.3 when it origanally had a 2.8 the truck never ran with the 4.3 former owner said it would crank but it never did for me i was just wonder what all i would need to get it started wiring wise

I would contact Painless performance, and just ask for a new underhood wire harness.
They probably won't have one made up but they'll be the best source to help you out.
http://www.painlessperformance.com/

It looks like you have some potential with that rig. Good luck with the wiring