I'm slowly working on a 51 Chevrolet Canopy Express that spent most of its' life working for a window cleaning company. I've got rust on the interior quarter panels and the angles the floor bolts to were, for all practical purposes, gone. The one piece plywood floor was rotten. I found two panel quarter panels that I can use and started to work. I discovered that you can't take the floor out the bottom because where it intersects the wheel wells, the cutouts are smaller than the wheel wells under this point. Because I have the donor quarter panels, I cut the existing angle off of the left side and managed to get the floor loose. It's still in good enough shape to be a pattern.
What I discovered next is going to be a major problem for anyone working on a panel or suburban. With the floor loose, you cannot bring it through the rear door opening. The uncut width of the floor is wider than any way you can fit it through the rear door. I was able to bring it out through the side canopy opening on my truck, but panels and suburbans don't have that opening. From my experience the only way to get it out of a panel or suburban would be through the bottom with the body off of the chassis or by splitting it.
Hope this gives some insight into the problem. Whatever you do, don't screw up the angles on the side, cause you can't find them and you'll have take one, at least, out to get the floor loose.
It took me two years to figure out what to do. If I'd started out too quickly, I'd have screwed it up badly.
