1969 Dodge Dart Swinger 340
My , Diaphragm clutch pushes pretty easy. It uses the same flywheel and disc as the previous B&B, which was beastly to push.
You can also just increase the leverage of the overcentering spring. If you combine this with a diaphram PP the darn thing will almost push itself down. However, if you do this, you have to limit the clutch departure, so that the pedal truly comes back up. And that means a pedal-stopper on the Floor, and perhaps more frequent freeplay adjustments, mileage wise. I mean once a year if you only put a few thousand "normal" miles on it every summer.
I/m only 71 so my knees are still working pretty good. I too have a 4-speed car, so one day I may be going down this road as well.