Please update me on the fix to your igition problem.
I have a 76 450 that I'm having a similiar problem.
Several months ago I steam cleaned the engine compartment. Wouldn't start after that. Messed around for 45 minutes on a 80 degree day and it suddenly started (something dryed up). Not a problem again until the other week when I left it outside at the airport for a week (normally it's parked in heated garage). Car had no ignition. I noticed the wire from the ignition box to the lower part of the distributor was in very poor condition with numberous cracks and chaffing to what appeared to be the core. While trying to do a quick repair I noticed this wire has an inter-core wire with insulation and a second layer of wire around it. I tried wiring the inter to inter with one wire and outer to outer with another. It seemed to fire just a bite, but never started.