It could also be a cracked distributor cap. I had that happen, loud backfiring, brown smoke blowing out of the air breather. I thought it was the coil, but the cap was cracked. I did have vapour lock about 15 years ago when I drove the 11B to a car show in Michigan. It was over 100 degrees farenheit for the entire weekend and it was hard to start when the engine was hot. I didn’t do anything to the engine and haven’t experienced it since. But do check the cap.
Larry Lewis