I also would suggest not just using hardware store grade bolts, like grade two or something. It might be overkill, but I use grade eight. (will have 5 little lines on the head surface) Our local Ace Hardware carries a terrific selection of grade eight stuff, and I keep cleaning them out......use them everywhere.

Not sure if grade five would work for a tranny to engine, but for the slight difference in price I'd go heavier.

Don