Torque convertor and detonation
Engine load, car weight are factors; doesn't ping in neutral correct?
I doubt a smaller c'ter would help & it will use more fuel because of the slippage.
[1] Get the engine running as cool as possible; heat is the enemy as far as detonation is concerned.
[2] Block or partially exh xovers in the intake.
[3] Rig up cold air induction
[4] Slow down the dist curve
[5] Retard the cam 4-6*.