you can never have too much cooling for the trans, a cool running trans, say 170deg, will last a hell of a lot longer than one running at 200deg.

measure your space where the trans will be installed and get the largest cooler that will fit. the bigger the better, you really can't over cool the trans, and a cool trans is a happy trans.
to install, break the trans line that comes out of the radiator trans cooler, (hahah what a joke cooler), and coming from the trans line you just cut, run it to one of the openings on the new cooler, then the other opening on the cooler attatch it to the other side of the trans line you cut.

so it will flow like this:

in the radiator, out the radiator, in the trans cooler, out the trans cooler, to the trans, that should cool off the trans a whole bunch, i hope that made sense, it's way past my bedtime.

good luck,

allen