you can probably score a basic dwell meter pretty cheap. It is important because it tells you how long contacts are closed for charging coil. Point gap can be correct, but if the cam is worn or even the point block your dwell will be off.
I suspect a worn cam (the one in the distributor) like I said above. On my buddy's 340 we swapped a cam from a different distributor and the problem went away. That's why you need a dwell meter or swap the cam with one another distributor.
