It took a while to find the problem, but it was with the distributor all along. It seems it was regraphed for a race motor with lots of initial advance required & a restricted amount of total advance. Or it was worn out. I replaced it with what was sold on E-Bay as an L series brand new distributor, but is more likely to be from an E15. Swapped the gear & plate on like the electronic conversion, got a GT40RT transistorized coil, dropped it in at about 10 degrees & the car is driving properly again, not stalling, etc.It's been really bad to drive seeing as the clutch started slipping due to the problem & was replaced with one of those heavy duty ones in the pink box. No torque off idle plus a heavy clamping pressure made every standing start an 'adventure'. So now the 'quick' engine swap seems to be right, it's time to get the A15 repaired. I think a 70 degree cam, 77mm pistons & such could make enough power to make this clutch necessary. Thanks again to John Mac for his suggestions, but it seems all the swearing I did at the carby should have been directed to the other side of the rocker cover.