When considering retro-fitting new disc brakes on an old drum brake car, what is the importance of the number of cylinders/pistons in the calipers? I have heard of benefits of "one is best" and "the more the merrier."
The regular single-piston factory calipers from the '73-up cars work just fine, I have them on my car. If it's any indication, the factory disco'd the KH 4 piston calipers in '72 and went to a single-piston caliper in '73. Less parts to go bad, similar amount of surface area.
If you want to be able to stop and feel like you could be thrown through the windshield, maybe get the multiple-piston calipers and huge rotors. Really though, as long as the rest of the brake system is up to snuff and dialed in, I personally wouldn't think there's much difference between single and multiple for normal driving.