Stamped a bunch of custom frames myself. No problems, even with out of state police inspections and customs office on export. Amen and Santee sent unmarked frames. The expectation was you would stamp the numbers from a donor bike into the frame and destroy the donor frame. It was very common from the number of stamped frames I see. I like OEM plates, but if a bike doesn't have one, it isn't a deal breaker. It will title, insure, sell, and ride, just like any other.