If anyone else cares to try this...
My son and I just converted his 1995 Jetta's rear brakes from drum to disk after he blew a rear wheel cylinder seal this afternoon. We had another Jetta with rear disk brakes in the driveway that he hadn't finished stripping for parts. Doing this conversion was planned, actually, but we...um...advanced the plan a bit, rather than buy a wheel cylinder.
The stub axles and caliper mount all fit the existing suspension, which was a pleasant surprise because it avoided changing the rear suspension and realigning it. With a bit of careful re-forming the brake lines fit as well. The front/rear brake proportioning seemed fine to us after the conversion with the existing rear brake pressure valve; i.e., the fronts lock first but they all lock up. The parking brake cables must be changed because the ends are different. The caliper hose mounts snap on from the bottom--don't try to remove them from the top or you will probably break one of the tabs off.
Pretty straightforward and easy overall. Anyone with rear drums could do this easily with junkyard parts. Stub axle, axle seal protector, splash guard, caliper mount, caliper, brake hose, hub and rotor (with wheel bearings, thrust washer, castle cover, and cotter pin), and brake cable are needed on each side. About 1/2l of brake fluid sufficed to fill and bleed the system afterward (the rear lines, of course, were completely empty).
Oh...and my son reports that the car stops much better.
JRE