Thinking of converting to Manual Brakes

A larger bore master cylinder will increase the leg effort needed to stop the car.
Agree, and what I said.

... Mopar put the "soft" pedal small piston MC on the power brake cars -- who knows why?
Mopar typically put the ... smaller bore units on the power brake cars.
Should have been the other way around.
Not when you consider the lever ratio in the stand-off brackets (as I said).