HowieE,
On my 75 the problem was an unknown leak had rotted out the floor and the bolts were missing
apparently they had rusted and sheared. If yours is built the way mine was (and no reason not to believe it) there is a large steel plate at the front. There is an aluminum channel that sits on top of the plywood. This whole assembly is thru bolted with 2 good sized bolts. If the bolts are loose, the plywood is bad, or the bolts have pulled thru the channel you will get problems like you have.
Here is a Picture of mine with the plywood out. The big black thing in the center is the steel plate. The bolts go in about where the frame comes up at an angle.
After taking another look at your picture...are the rivets in the plate sheared? Do you have the plate?
Aaron
