I have been battling with a similar problem. Managed to solve my problem this weekend. I do not own a dwell meter, so even though I had adjusted the points to the correct spec, the engine still misfired. I suspected wear on the dizzy shaft, but without a dwell meter this was hard to determine.
I was told of a trick one can do with an ordinary timing light. Set the timimng with the light connected to #1 spark plug, then test the timing with the light on the #6 plug. If there is a difference in the reading, it is a sign of dizzy cam wear. All I did was adjust the point gap till the timing reading did not change between the #1 & #6 plug, and bingo, no more missing. Point gap dropped down to 0.015'. I found it to be very sensative to the point gap, 0.016 caused it to misfire.