Reduction of flow can be an issue when stacking coolers, you want to see 1 quart every 30 sec min at the return line. IMHO you are waisting your time to run both coolers. They both mount in the same location so you would have to fab a bracket to mount one of them. I have a 2000 without the oil to water cooler in the rad. My temps dropped a solid 40 degrees. I have been towing very heavy and slow up some steep tight switchbacks and the warmest I have seen is 170 and tht was with 95 ambient temps. Toss that small cooler in the trash where it belongs!!
NCH