I have a 6 Pack Bird, too. I had Holley did the carbs. DISAPPOINTING, Color and warped base plate.! All American Barb in Florida is a great choice, too!

Did you have Repop Harnesses on car when it caught fire?
Ironically, I have a 65 Coronet Convert I am building/built. Evans Harnesses originally.
Got the Engine Bay detailed and all running well!
Let it idle for about 15 mins then took for a drive.
Car caught on fire and did the same damage as yours.
I had blamed the situation of possible mel;ting of Holly Plastic Sight Plugs....(Ethanol)
Nevertheless, I bought harnesses from MH (Year One) this time.

Don;t know the exact cause but I am eliminating possibilities.