[Phx Mike]

Robert as my wife said as my car was being hauled up on the flatbed once a couple of months ago - "the good looking ones are always high maintenance".

As stated above - the old guidance on timing was always to remove and plug the vacuum advance and set initial timing (everyone these days seems to run a lot of initial advance but most of the OEM guidance was always around 10-12 degrees initial with the vacuum advance plugged). Then get your vacuum checked out. Vacuum advance if working correctly will get you better part throttle fuel economy when cruising. It may also help the car run cooler in those conditions. I am not sure why this was not causing a problem before, and is now, but I think your theory about the distributor advance plate being stuck previously and now loose is a plausible one. It may just have never been working before, and now it is. If you are getting too much advance with the vacuum advance connected, you may need to change the vacuum canister.