they dont want to touch it because they cant guarantee it. with an old car you are likley to have many problems and they dont want to get "married" to your car.

your best bet is to get in with a welding crowd. if there is a local car club, join it. if you are not already full of classes and/or a good job, maybe take a welding class at the local college, or get a job at a muffler shop or welders shop until you can fix it up yourself, or find a friend to help. most shops aren't going to touch it unless it is a place that does 'ground up' resto, and then that's what they'll want to do...and it's big bucks.

if the rail is rotted, you should look into all of the metal around it, and if it is rusty, inspect the metal that attaches to, etc...depending on what you find, you can decide if a parts car would be a better doner than new parts. just about the whole car is available in reproduction parts.....or you could just cut it all out and tub it.