If you had the original motorcycles vin # and plates you could just keep buying tags for it and put them on the build. You would just need a bit of frame with vin#.
The biggest hurdle would be an inspection on the street, for sure you will get stopped. I guess if you had registration and tags and all the safety equipment worked you should be fine.
James and Colleen Tucker.
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DMV paperwork/room rental/motorbike/vehicle buying/Travelers help