You're about 3 years too late in the asking for mine. I sold a fastback that would have been perfect for such a conversion. In fact the guy that bought it off of me was going to build a custom car out of it so he didn't care about the originality of the car and bought it as a roller from me. Though I'm glad I sold it back then and not trying to sell it now given the market on these cars at the moment.
My biggest tip to you is not to spend too much money on the car itself or you might as well go out and buy a Shelby outright. I don't know what your situation is and whether you'll be doing all the work yourself or outsourcing it. If you send all the work out, body work will add up fast and a good paint job will be in the 6-10k+ range. The Dynacorn bodies become a pretty good investment for such a build because it doesn't take long to spend over 10k in body work prepping a 30+ year old body and since you're already making a conversion you need not worry about the originality. The only decision will be whether you want to make a 67/68 or a 69/70 Shelby because I believe both bodies are available from Dynacorn.