Do you have any of the builder logs, airframe and engine logs? I would think that there would be some info on the builder and plane's history you could glean from those? Also, the original builder should be on the identification plaque, usually located on the tail or somewhere on the setback bulkhead? Do you have an EAA chapter on your home field? Are you a member? An EAA tech counselor would be a good one to go over the plane with you, especially as you try to complete any work on it. By the books, you will need an A&P (or the original builder) to sign off on any alterations or major repairs.
Richard K monitors this group. Any insight you can add Richard?