Upgrading from kelsey hayes to???

BobW said
Hydraulics is hydraulics is hydraulics!
Spongy brakes are generally due to leaks, a bad master cylinder or improperly sized master cylinder.
For comparison, I have a '37 Pontiac street rod with an original '74 Mustang II front clip, weighs 3800 pounds. I upgraded the original 9" discs to 11" GM metric discs & calipers along with a 9" dual diaphram power booster. Stops on a dime with little effort, almost too much power assist!
My '64 Valiant has the KH conversion with a manual MC. It stops just as well, with just a bit more pedal effort due to the manual MC.
The only way to upgrade braking performance, if it's actually needed, is to get better pads and/or increase swept braking area (contact) which means larger discs. I don't think you would see significant gain in swept area by just changing calipers.

Thank you! Your pontiac sounds pretty cool, I recently gave my dad a 1930 desoto 8 sedan that was in finish assembly after a frame off restoration and he decided to street rod it, its in the process of having a modern hemi and bolt in mustang 2 front end system, Ill likely just rebuild the calipers I have, it seams like most of these aftermarket kframe/coil over suspension systems sold for abodes are just a modified version of the mustang 2 front end.