It is .004
The spark plug gap range for the non-Boss 302 is 0.032"-0.036".
Spark plugs
According to one of Fords websites : For a 1986 Ford Mustang , 5.0 L / 302 cubic inch V8 engine : The spark plugs are gapped at ( .050 inch )
The recommended spark plug, for a 1984. Thunderbird 302, V8 engine, is a champion spark plug. The spark plugs can be purchased at most auto-parts stores.
.050
check or change the spark plugs & wires
Start with distributor cap/rotor, spark plugs and spark plug wires.
According to one of Fords websites : For a 1973 Ford Bronco 5.0 L ( 302 cubic inch V8 engine ) ( The spark plugs are gapped at .035 inch )
402 and 302 are the Cubic Inches of the engine, the more cubic inches the more horsepower and torque the engine produces, so to answer your question the Mustang Boss 402 would have more power
According to one of Fords websites : For a 1968 Ford Mustang 5.0 liter / 302 cubic inch V8 engine : ( the spark plugs are gapped at .035 inch )
.050 inch spark plug gap - 1986 Ford Mustang 5.0 L ( 302 )