call CPR california pontiac restorations. located in santa ana california they will have everything you need.
I think the 8 lug hub and drum used from 60 to 70 and unique to Pontiacs can be used. I don't know if the bearings are a direct bolt on or would need adaption. A simple switch to 59 spindles would aleviate that though. In 65 the front brakes were widened and might require changing to those spindles. I believe the rears are an easy install just by sliding on the drums (might require using 59 or later backing plates) and the rears stayed the same width in 65. These are probably the best drum brakes offered on a production car. I had the rims on my 65 2+2 widened to 8" and chrome plated. Didn't look to bad in the early 70's, although I had to radius the rear fender openings. A 58 would probably have enough room for 8" rims without any difficulty. There was a mid-sixties Pontiac at the Portland show a couple of weeks ago that had large diameter aluminum rims installed on the 8 lug drums, looked really good. I've always wanted to do that.
Sorry, I dropped my camera (digital) getting ready to leave for the show, so naturally it croaked, and I didn't get a single picture. Murphy's Law I guess.