Cheap projects are cool. Anyway you go with it is how it's suppose to turn out. Even better, if there's some money to you in the end ! Good luck with the build.

Around here(South) we have some who cut up old frames and use the parts to make "one of a kind" builds, imaginations are their limits. That serial number could be from one such bike before it was cut up.

Still a cool project where ever/whatever the frame started out from.