"Mild street build" 440.
Would need more on the cam to plug into 'pipemax' but from past experience I can tell you that discplacement plus power band rpms are primary factors in determining the sizes needed. Guessing that the rpms of interest and peak Hp is below 6000, probably below 5500, would favor a smaller diameter (like 2.5"). 3" is a big jump up in terms of cross sectional area. I'd not do that without more data or as an experiment. If so, I'd test it from the collector to the first interuption (H- pipe, X pipe or muffler).
H-pipes and x pipes are somewhat useful for 'sharing' the mufflers, but measurable value seems to depend on placing in the right location to create harmonics that help in the rpm range of interest.
My guess is the factory either found a performance advantage with H-pipe and/or used it to break up a drone resonance.
