If the car will be driven in a cool/cold climate at all, I'd recommend installing the trans cooler in line with and just after the factory cooler.
Here are some pics of my B&M 28,000 GVW cooler on my 90 XR7. Since it is a warm weather only car, the cooler completely bypasses the factory cooler.
The 24,000 GVW cooler on my 94 LX is routed in line with the factory cooler, since I drive that car year round (and it gets pretty cold here in the winter). I don't have any pictures of that setup, but it's mounted in the same location.
I have the 24k# on my Cougar, and I have no heat exchanger in my radiator (Cobra Radiator), but even here in MO when it was in the 30's or below, the trans still lifted the temp needle a little...
'95 Cougar - 2002 Explorer engine, 2004 Mustang PTP2 PCM
PI 4.6L 95 XR7 Cougar: [email protected]
2004.5 Silverado Crew Cab/Long Bed/4x4 6.6L Duramax: [email protected](Weighing in at over 7200#) on 10/19/2007
Dyno - 446.4RWHP/820.2RWTq on 6/13/2008
Pulling - 300.9' 3rd place finish 8/2011