Does anybody know what disc brakes will fit on this car?

It is usually cheaper to go the kit route rather than utilizing take-off parts from a later model-

-Stainless Steel Brakes-

-is one such supplier.

Have you talked to -Master Power Brakes-?

They can make adaptors to fit calipers to your spindle. They also offer a kit for a 1961 Chev. Maybe they can adapt the kit to a Pontiac.

Just a thought look at corvette spindles from the early cars.I think they may just bolt on with disc and all. I seem to remember the spindle is the same style but i had to adapt the rear wheel bearing and after all the work noticed that the whole spindle with brakes worked . i did this a long time ago but check it out.Look to see if your balljoint points down with the spindle under the lower control arm(like the vette) I find the earlyer vette stuff pretty cheap(cause spindles dont get checked for matching # LOL )