Another case of were the restoration group moved to an easier to get part. But I have seen a flat tooth type lock washer on the 4 Speed bolts to the bellhousing. Not star type though.

Yes automatics are captured conical washers tranny to block, with a unique hex head. I believe the correct length are 7/16-14 2" and 1 3/4, 3/8-16 1 7/16" and 3 at 1 5/16" for the automatics. The odd 1 7/16" is based on the trans housing having a thicker section at the one 3/8" hole above the starter. The difference in 7/16 length is one ear of the block is thicker by 1/4".

Same reason the 4 speed bell housing has one longer 3/8" bolt.