I had a similar experience with an Ford inline six. Backfiring through the carb, fouled plugs, etc.

I thought the timing was off so I checked chain tension, Compression, etc. It turned out to be a faulty condenser in the dizzy.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)