The Osborne assembly manual calls for 20490-s for an automatic v8 as does the excel spreadsheet by Jim.
Chris,
Thank you.
Another book I have calls for 20534 which according to Jim's is for the six cylinder.
True. V-8 engines used 7/16 inch hardware, I-6 engines used 3/8 inch, to attach the bell housing to the engine.
I have two type of head markings for the 7/16 inch bolts in my pile of junk, none (as in
none) and "F". These are grade 2 bolts with no head recess, flange - nothing, and as such are supposed to be available from any source, at least in the '60's. I can't tell what cars they came from, junkyards are noted for keeping track of every nut and bolt, but with a sufficient quantity (mostly San Jose), no head ID is the norm.
Jim