The short of it is that the head won't come off. I followed the BSA issue shop manual's instructions to the letter and the head boss between the inlet rockers fouls the backbone tube before the head comes free from the front studs. Rear studs clear by 3mm or so. I don't believe that's correct. I tried very way to move the head off of the front studs and the boss hits the frame every time.
I would appreciate advice regarding how I may properly remove the head per the manual, or god forbid I have to remove the cylinder block and head as one. That I don't regard as a viable option.