Hi Harris,
Firstly thanks for that image as it certainly casts some more to the story.
So sorry to be the bearer of bad news to you, but your chassis has quite a few fatigue fractures showing, especially to the right hand rear bolt area and these "must be corrected" before you do anything else. After doing that I wouldn't waste any time putting an old thumper back on to it as you'll just end up with more of the same.
Once done with corrective surgery I would only put a new Briggs or similar style engine onto the chassis so as to avoid more of the same happening and merely shortening it's life.
Cheers,
BB.
PS. If you remove the aging paint around the bolt holes it will reveal the fractures. I know that not what you want to do but not doing the job is merely placing a band aid over what will turn into catastrophic rail failure.
