is there a difference between 6 cly and v8 manual pedal assemblies?

Yes, there are three different assemblies. They are 6cyl., v8 and heavy duty v8. Basically- light duty, medium duty and heavy duty. They all interchange but were matched to the engine/clutch in the car. Mine, '68 cuda 383, is the heavy duty where the swing pedals ride on bearings not bushings and the over-center spring is heavier with additional bracing.