Well I far from an expert, but if you are going to be running a GTX 580 and an overclocked 970 you are going to need a fair amount of radiator to handle all that. Something like a 360mm radiator of good thickness or a 360 and a 240 on the back of the case would be nice.
Pretty much, you will need as many radiators as you can fit inside (or outside) of your case. If you can try to buy decently thick ones e.g 60mm
antec 1200 is a pretty big case, and with the amount of hardware done buy a crappy 250lph pump, this is not the place to save money.
fan setup's on the radiators is a big issue, the more fans the better really.
For a good overview on how to set up water cooling, Tom has already done a short set of videos. They are great and will really get you to grips with everything you need to know. When you are watching the video, just keep in mind you are going to need far more kit than he is using because you are cooling far more components, but the theory is the same.
Video's can be found HERE!
Watercooling Part 1 Watercooling Part 2 many thx for your time and effort bro
I have no experience with the antec 1200 so am not quite sure how much you can fit inside But I'm sure some of the other fellows on this fine forum have 1200's
Also, a good idea to get inspiration and to find out what is possible with your case if to look around on the forums, maybe in the Rig Gallery, or in the project log. There is a gold mine of knowledge in there. And if you can't find any watercooled Antec 1200's then just good "Antec 1200 Watercooled" its bound to throw something up.
Good luck.