I added a B&M #70268 (13k btu) cooler 20+ yrs ago. It is 11" x 7 1/4" x 3/4" thk and a stacked plate cooler. Regretted later not having a 1 1/2" thk piece, so bought a B&M 70266 (20.5k btu) that is 11" x 8" x 1 1/2" thk.
Later by-passed the rad cooler, then a few years ago said f...it and re-installed the 3/4" unit in tandem. They are mounted to some scrap channel pcs about 1" in front of the condenser.
Have an aux filter below these mounted to the rad rebar. Also added a temp sensor at the aux filter and monitor temps on an Autometer trans temp gauge. Have not had any issues, but I don't beat on it until the trans holds some heat.
I'll take a pic in the next day or 2, here's an old shot of the filter.