Ok, the car is a 70 challenger with fast ratio steering, so not sure if headers will fit or not.
The car is a standard.
Rear gears are 3.55

The reason I said 400hp is just to clarify that I'm not looking for a stroker motor, just a point of reference. Mild build.
Since the motor is in great shape, I was hopeing to get better response.

Are the 906 heads a good option for this motor or would bolting on different heads make a big difference?