OK, if you look that close, you will notice in these pics that the rear roll bar is not all welded in, it is now, just had to finish fitting these parts and remove them prior the welding before I bury something I can't get to.
This is the seat back support, and likely the seat belt mounts by the time I get it done. I will make a seat belt mount as a gusset between the lower 1.5 x 1 and the tube. The seat belt will go over the tube on the outside of the square tubes, making about 7.5 inches between the shoulder belts.