Slys240z

I have a 91 gmc truck with a 305 TBI. Just wondering how to do all this with it being TBI. Prob has a compter. Which wiring harness do I use. The truck one or do I modify my 76 z harness. Have no clue and would love to know how to do this. Motor runs great so I would love to keep it. Vids would really help out. Anything at all would help. Please help me. I am so lost. LOL