SBC banging @ 3200 RPM

I have 30 over 340 with eddy aluminum heads, 3310 Holley vacuum secondary, mild purple shaft cam good to maybe 5000 rpm, a built 727 tranny with 2500 stall, MSD mechcanical dist, E3 plugs, MSD 8 mm wires. It idles fine. At 3200 rpm the engine as developed a bang or mist fire. Oh, I did change recently to a new style coil it’s blue and squared shaped mounted on the passenger wheel well that MSD says works with the MSD 6AL ing box. It’s an older box mounted in the car to heater box. This is not a fresh engine build it driven only on weekends an older restoration,

Thinking a new cap and rotor, suggestings welcome...