"That's the only name they ever gave me."
- "A long time ago in a galaxy far, far away...."
Looking at the chassis corrosion again, given the issue at the front that @PhillipM pointed out, and the fact that you have this firm down the road, I would seriously consider cutting off the rear axle back and rebuilding the tube chassis with new tube using the existing one as a template. In the grand scheme of things, you wouldn't need a lot of tube, it shouldn't take too long to fab and you would end up with a chassis that you'd have complete confidence in.I have a firm down the road from me that have a mandrel bender so will get them to form me a new pair up
Please don't take this as cristicism, it's just my opinion as I wouldn't have complete faith in the current chassis