904 Transmission Stopped Going Into Gear

Yikes!! That looks DANGEROUS!! Hey if nothing else, just notch a 2x4 about three feet long and attach it to a pivot on your bench. Your C-clamp business is outrageously toying with a visit to the ER. Ya, that's a three plate drum. You can still put four into it if you use a lower pressure plate from a forward drum on top; if you can't return it. Those ring surfaces look a little sketchy.