The only radiator/pump combo that I know of is the Swiftech setup, which will be solid quality since it's basically a similar version of their normal radiator (with a reservoir built in, the reservoir makes it more difficult to bleed air out of the system I've read, but I don't know the specifics about that), a normal high quality pump, and you can put whatever fan you'd like on it.
Of course, the Gentle Typhoons are recommended, but it's up to you. You may be able to tie a fan into the normal fan plug on your video card if you want a controlled fan that follows a fan profile like the stock one does.
All of the major radiator companies seem to make single 120mm radiator variants of what you see others using as 240mm or 360mm, so that shouldn't be a problem, and a single radiator probably scales better than 240 or 360, so you'll probably only get a reduction of maybe 50% versus a 360 or something, though I doubt there is much if any hard data on that. (I base that off of the reverse, when people scale a double to a triple radiator and don't get a 50% boost, but a smaller one).
You shouldn't have a problem managing under 60c for a 6970, even with overclock. Watercooling is very efficient on GPUs versus CPUs, since the GPU die is much larger, so it has more contact with the cooling block. Just make sure to get VRM heatsinks and keep them cooled!
I can't wait to get my new loop built and cooled. I've got an old 120mm radiator and pump and crap that I've got to sell, which hopefully will offset the new kit. It's funny that I'm switching to CPU cooling first, considering my current loudest component is my GPU fan (6950, no overclock).
Edited by Dr.GumbyM.D. - 4/11/11 at 12:26pm