I just completed a 4 wheel disc conversion using Baer brake parts. I researched a few different brands before settling on them. Like Kevin said, you'll need to get a master that is designed for 4 wheel discs, as well as a new distribution valve for 4 wheel disc. I installed an adjustable proportioning valve in the rear circuit, but probably didn't need it. Won't know until I really get the chance to bed the brake pads in properly and do a bunch of real hard stops, to the point of wheel lock-up. (they want a couple hundred miles of driving to get thru the rotor zinc coating before brake bedding procedure)
Regarding master cylinder bore size, 1 1/8" is the stock 2 W disc size. Baer recommends going smaller depending on your available vacuum & system. I went with a 1" bore m/c from 'the right stuff', purchased from Summit. I don't have a lot of miles on the car since the conversion, but the initial pedal feel, travel, and performance of the system is a huge improvement over the stock brakes. I almost went with the 15/16" bore m/c, but figured since I also have a vacuum pump, I would go conservative with the 1" and drop down if needed. It doesn't appear to be needed.
If you need part numbers, let me know & I'll find them.