I am doing this the other way, I have the '86 engine bolted to the '64 bellhousing. There IS one bolt that is different, and it's in a pretty important place, so I drilled.

The bolt in question is the lowest on the driver's side. It is right below the dowel pin. You should be able to drill through the hole in the block, through the transmission bellhousing. I'd suggest using a bolt and nut.

Using a modern engine mount system, where the engine is supported on each side and the transmission supported at the rear, this bolt (and the one on the passenger's side) is the most important one to keep the block and bellhousing together at the dowel. Using this mount system, one could leave out all the other bolts except the bottom two (one on each side)because the top of the transmission is pushing against the block. The bottom two are doing most of the work.

R.

PS: The LA is a direct descendant of the A Poly motor, has NOTHING to do with the B.