The 93 - 97 LT1 T56, and bellhousing will bolt up to pre '86 block, but you have to buy an aftermarket flywheel, and clutch assembly. They are not cheap. I bought my flywheel, and clutch from Centerforce and I think the price was around $600
Wier has a kit for SBC blocks that except either the LT1 or LS1 T56s : http://www.weirhotrodproducts.com/