The bolt size is 1/4 inch for the bell housing to block.
Assuming you are using a stock style cast iron 552 bell housing or a 553 aluminum bell housing, the bolts are:
5 - 1/4" by 1 & 1/2 inches (I think the originals were 1 & 3/8")
2 - 1/4" by 2 & 1/4 inches (one per lower side of the bell housing)
I have stainless on mine with stainless lock washers on these sizes.
If you have a horizontal mount starter there is 1- 1/4" by 1 & 1/2 inch from the bell housing to the upper starter.
There are two more from the starter to the bell housing -also 1/4 size - I have a vertical mount starter so I can't check the length.
Paul
The transmission is a 4L60 and my main goal is just to get the engine and transmission in place so I can start routing lines, wires, put the fenders back on, etc. Since the transmission isn't drilled for a top bolt, I'm guessing I'll need 4 of the 1/4" by 1 & 1/2 inch bolts.
I don't have a new starter and may opt to rebuild the original, but that isn't a right now problem.
Long term, I will probably get stainless, (lock washers for sure), but for now, I just want get things in place and don't want to beat up my shins walking around the engine.
Thanks Paul!