We b OLD,
I wouldn't think an electronic problem (the Pertronix) would take 2 months to gradually develope. Electronic items usually just crap out instantly...in the middle of the night on a lonely road. The coolant leak is interesting, but the valve cover area is too high for a typical head gasket failure. Why don't you put a timing light on it and make sure you have fire as it tries to die. Even as it fizzles out you should have timing light output if the ignition is working properly. A compression check would be next. I had an old 216 with a blown head gasket and it did some of the things you describe, especially the backfires. A blow between ajoining cylinders and the water jacket is very possible. The carburetor has a high speed circuit and and low speed/idle circuit, when the idle circuit is plugged, the engine will run, but only at higher speeds. Remember, this problem has developed gradually so it isn't a sudden failure of a component but rather a condition that is getting worse.
Stuart.
