OK so I got the head back onto my engine today and assembled the cam shaft and chain.
At absolute TDC, with the forward half (the non-tensioner half) of the cam chain pulled taught, this is the line-up I got with the marks on the camshaft sprocket:
The marks are of course supposed to line up exactly with the gasket mating surface, but mine didn't. Definitely not an issue of the chain being a tooth off... it was too close for that. But it's OFF in the way that it is is consistent, I believe, with a stretched cam chain.
Time for a new cam chain.... right