I went with Baer Brakes Super Street system in the front, fits behind 15" wheels with no problems. Easy install, great performance, and I think it was around $900 with everything needed to convert from drum to disk. Looks good, too, with the drilled and slotted rotors and nice aluminum calipers. I left rear drums stock, I don't see a need to upgrade the rear given the weight distribution of the car and my plans for driving the car (cruising mostly).
That being said, if my car had been a stock disk brake car I would have left it stock, I think the stock system is fine for typical use on these cars. I converted my '71 Javelin to front disk with a stock set of parts, mostly because I couldn't find a reasonably priced aftermarket kit, but those stock brakes work great.
'68 GTO, 400/TH400, AC/PS/PB/PW, hideaways, Hurst dual gate
'72 442 'Vert, 350/TH350, AC/PS/PB/PW
'74 Corvette, 383/4-speed, 450 hp, restomod
'71 Javelin, 304/3-speed
'70 Cougar XR7 'Vert, 351W/FMX auto *SOLD*