1936 Bolts and B Pillar rivets
 

What bolts were used to bolt through the floor pan to the angled part of the frame? They are 5/16" fine thread, go into cage nuts, but what head do they have? Was the B pillar riveted to the floor pan originally? Kinda looks like 2 - 1/4" rivets in each pilar at bottom foot. Thanks for all your help, in advance.