My 59 model 3800 had 18" rims with a removable bead on one side, but they were not split. There was a small oversized area on each removable ring that allowed it to be pried off the wheel by sliding it a little sideways. It was vitally important that the mating areas were clean, and not rust-damaged, as the mating surfaces had a minimal amount of contact area. I notice some of the tires on yours are showing lots of bulge in the sidewall area, indicating very low pressure. DO NOT attempt to reinflate those tires without a complete breakdown and inspection! Even a slight misalignment of the side ring due to insufficient inflation can cause the ring to blow off with no warning if air is added. There are several TONS of force applied to the ring at full inflation pressure, so don't take any chances.
Jerry
