The short of it is the head won't come off. I have the factory issue shop manual and it's stupidly simple. However, on my bike, the head boss between the inlet rockers fouls the frame backbone tube before the head can come off the front studs (the long ones). I've got 3 mm clearance on rear studs. What is going on here? Removing the cylinder and head as one is really not an option. The head should come off clean with engine in frame. I'd greatly appreciate advice from those familiar with late model BSA unit twin top ends.