You're going to have to go to a machine shop regardless. I'd ask them what is the best route to go. Also if you go gen 3 block there are variances like I said before. The biggest pain in the ass was finding a gen 2 oil filter adapter. Goodluck with everything
Are you getting a new shortblock. I just swapped to a gen 3 shortblock. You need gen 1 oil pump, opgs, pickup tube, gen 2 oil filter adapter and oil pan. Then all your new timing components gen1, gen 1 head gaskets and gen 1 rear main