Yes, I am now red-faced, but since it may help someone else, I'll confess. My Cub would not start, as the thread details. I even went so far as to pull the head and adjust the valves. Cylinders and valves look amazingly good. I put it all back together and still no start. In desperation, I went back to basics and checked spark timing for the nth time, and made sure again that the wires were on the distributor in the right place and order. They were not! I got them on right, and behold, it started. I still have no idea what the original casue of the problem was - unless some kind passerby swapped wires on me, and I guess that is possible. I guarantee that if it happens again, that will be one of the first things I look for rather than the last. And yes, I have now numbered the wires and the cap with white paint. AARGH!
-Ortis: a thousand years behind Sound Guy, but may someday catch-up a little.