So long question, but is there any difference in the piston action of a MC that says it is specifically for a Power system vs an MC that says it is for Manual system?
It depends on the rest of the system. If the power booster operates through a bellcrank, then the leverage changes.
According to Chrysler's tech pamphlets, some similar looking master cylinders had slight difference in the front/rear piston. But aftermarket and parts store master cylinders are often consolidated to minimizing stocking. They don't worry about slight differences like the car manufacturer had to, as long as it functions close enough - however they define that.
Previous post about Master Cylinder different part numbers. How come all my manual drum cars have disc master cylinders?
I would contact Scarebird and go with what they recommend, unless there is a red flag that their recommendation is poor.
