If you have the trombone cooler in front, and it's almost adequate, then the smart upgrade (in my opinion) would be a Carrera cooler in front, with a fan if you've got room for it. Putting the cooler where the AC condensor was is going to restrict airflow to the main blower (which, admittedly, the condensor did as well), heat up the air that's intended to cool the engine, and also add weight in the rear of the car, where you don't want it. Up front, you wouldn't be doing any expensive experimental plumbing, also.
------------------
Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net