As already mentioned.. stacked plate style is better.. Easier to mount and cools better.
Adding a cooler in front of the a/c condensor shouldn't affect the radiator cooling much if you mount it correctly. With the tube/fin style coolers you normally use the push through mounts which puts the cooler too close to the condensor which can make the a/c not work as well...
Putting two coolers in front of each other in front of the a/c will block too much air (I tried it that way already)..
I have since put two permacool trans coolers (stacked plate) next to each other in front of the a/c condensor (one 24kgvwr and one 30kgvwr cooler).
I also put a fan from a geo prism in front of one of the coolers to help in the stop/go traffic.
~Mark