errrmmmm ... if George is in Germany then answers about US licensing are only relevant insofar as they might affect the export of this item.
unless US Customs would be likely to impound it as stolen, it probably doesn't matter. Of course, if they are, it's very much to the point.
how TuV would view it, I have no idea. My feeling would be that you could either;
(a) register it on a Q plate in the UK, provided you had enough receipts for the main components of the build-up
(b) get a UK age-related registration, but this would be difficult and unlikely
in either case, you could then get a German registration based on having a UK registration and the US provenance would be irrelevant.
Holland has been a centre for registering bikes of dubious provenance for as long as I can remember, and I passed my driving test in 1971....
Mongo only pawn in game of life