Length of tranny cooler in a 26"OEM rad and

where to put an external tranny cooler if you have an A/C condenser in front of the rad already? For non A/C cars,wouldn't putting a external cooler in front of the rad block air flow to the rad? Just wondering if OEM internal tranny coolers were all the same length or was length dictated by rad size? Car is a 73 Dart Swinger with a 84 318 and a lockup 904.
Thanks 318MG