I have back problems too, Magnumforce, so I have some understanding of your pain.
You've worked so hard and achieved an enormous amount in a very short time with this lovely old car.
A wise man (on here I think) once advised that if it all gets too much then it's a good idea to put a cover over it and walk away from it for a couple of months, or however long it takes, and have a good rest from it. Then make a decision about whether or not you want to continue the work in a few months time.
Enthusiasm and physical ability are often renewed after a good rest. It would be a shame to sell it after all that work and then to regret it later. Good luck what ever you decide.