Can you locate the original builder? He/she is the only one that can apply for the airworthyness certificate.
Actually, this is not true. Anyone can apply for the airworthiness certificate, but they must be prepared to prove that SOMEONE built at least 51% percent as "an amateur". If you are not the original builder, you'll never be able to apply for the repairman certificate for the plane, though.
You have prove that you built 51%. I'm not sure a tare down and reassemble would satisfy this
AFS-610 told me that they do not consider taking an already built plane apart, and reassembling, to "count".