This question come up on Stovebolt quite often. A Stovebolt is pulled out of field or there is only a bill of sale. In you case you've built it. The DMV or state highway patrol should be able to inspect it and verify that the required safety equipment is there and issue a VIN. I just googled custom built for Alabama and they do have a process.
http://www.dmv.org/al-alabama/custom-built-cars.phpUnfortunately they do seem require an old VIN or bill of sale, as you say. There is on the bottom of the page a link to ask the community you might try that.
Larry
