I have recently stumbled over a superbly looking bike for sale in Germany.
In the small ad it is described as a BSA 65/ A70 and the seller tells the story that in 1971 the American BSA dealer Donelson in Missouri had built up eight A70-engines in dry frames as Spitfire look-a-likes.
I gave the seller (which seems to be a very nice bloke) a call and asked for the engine-#. I had expected the usual SRM
/Devimead-whatsoever big bore engine and was surprised. It appears to be a genuine A70L-engine # stamped in August 1970. He claims the frame-# matches it, it looks like the bike's chassis had been assembled from parts and the engine-# stamped onto it.
A quick search via Google brings Donelson as a fromer dedicated BSA dealer, the bike's engine-# seems to be listed here
I never heard of such dry frame A70s, did you?
The bike is priced quite high but given the number of A70 and the condition it seems not that bad.
Lucky me, I have enough bikes, so I can stand the temptation.