Yeah, as some above have said, try to find a better starting point. Sure it can be done, but unless you have a lot of time and all the fabrication equipment, and a lot of patience, you will get discouraged.
With the amount of $$ you will need just to get that lump to a decent STARTING POINT, you could be miles ahead by just getting something with less rust.
On the other hand, it can be done, and the sense of accomplishment by doing it will be fantastic.....just be ready for a very, very long project.
Good luck....
Tim