OK, I'll try to take these responses in turn:
- Gas cap: I did make sure the gas cap was venting. Fuel flow is good down to the carburetor.
- Modern distributor: Yes, it is the modern points and wireless plates. I've had trouble with them before, but I looked them over pretty thoroughly this time and can't see any problems.
- Condenser: Could be the condenser, but then why does the spark test good every time I check it? I checked it with the engine off and on. I guess I can't be certain it's working 100% of the time.
- Fouled plugs: I treated the plugs with a wire brush after I pulled them and found them to be fouled. Should I do more?
- Compression check: Do I need a tool for this or can I check it by just sticking a thumb in the plug socket and turning the engine over?