As Roger says, Forget the yanks, keep them in Europe, the Spaniards used to pay silly money for bikes, they didnīt make many 4 strokes and BSA singles were imported here in the 50s.
The British are too tight to pay todays prices because they remember how cheaply they could have bought them and if yours are European restorations they might not be to British specifications.
Either way get rid of them now before it all goes down the pan.