I also did the disk brake conversion on my 544 earlier this year. I haven't put any miles on it yet, since I'm attacking the bodywork, but the brakes work well at driveway speeds. I had a lot of help from folks on the Brickboard; there are several sets of instructions floating around the web, none of which thoroughly explain every detail. One such site is www.bearmanmotorsports.com/pv.html You might find references to some of the others by researching the Brickboard Archives.

I drilled, welded, and filed the holes in the 122 mounting plate to fit the bolt pattern of the 544 spindle; I redrilled the two holes that were way off, and welded and filed the two that were close. I clamped the mounting plate to the spindle and used a nylon bushing purchased at Ace Hardware to center a small drill bit in the spindle hole that I needed to match, drilling from the back side, then used the spindle hole again to position the larger bit. I bought high-quality bits, and watched very carefully to keep the bits square with the spindle and mounting plate so as not to ruin either. A drill press would be better, I suspect, for the final drilling with the big bit. I had a front-end shop cut and weld the shock mount bolt so that it would clear the steering arm with the shock moved to the front. This is the part that I'll be watching closely once I start driving the car.