If you don't already know the pressure and spring rate, try to find out. After considerable discussion with a clutch specialist, I have come to the conclusion that "A" pressure plates, as well as early V-8 pressure plates, are being rebuilt by clutch houses with much heavier than stock springs. They then require much more pedal pressure than OE.
If anyone knows the wire size, number of coils, OD and ID, spring rate, etc., of a correct OE spring, it might be possible to find them at McMaster-Carr or Lee Spring.
Joe