Bellhousing to block bolts

[rechinca]

Trying to figure out what this bolt looks like. Mine was a mix of bolts, some with washers and some missing, none of them stock bolts. What should I have for a 350 with a cast iron bell housing for the 3 speed Saginaw? I have the bolts for the bellhousing to trans, just not for the block.

I have seen they are 3/8" - 16 x 1 5/16", but I have seen flange style and various others and some sources that say if using a certain bolt you must use a washer. Not that I am doing a restoration, but would like to use what the factory would have used on a SBC to bellhousing. Appreciate any help and pics you might have.