Thanks for all the replies. These bolts are for the rear axle flange to hub. One side is original but the other wheel has the original bolts replaced with studs, lock washers and nuts.The studs had to be removed because the wheel bearing race is removed by tapping on the race with a punch through these bolt holes. Removing the studs was a pain and I wanted to replace them with original style bolts like the other side.

I did cut down some grade 8 cap screws to come up with a functional replacement with the same amount of unthreaded portion. They will function fine. They just don't look like the originals because the old 1938 bolts have a taller head. Of course,no one will notice but me.