Excellent insight and thank you for measuring the temperature during normal driving conditions. This is great news. I still plan on doing the Magnefine filter but if no cooler is needed, that could be one less modification to plan for.
I have an M8000 winch between my valance and bumper, so I won't know how much space I have at the lower crossmember for a heat sink until I remove the winch (the heat sinks stick out like 5-6 inches). I might go with a ten-row radiator cooler or some other type of finned cooler if no space down...
The dual pass look similar to what some people have put on their 80 series. I haven't seen too much information in the 60s forum on this. Please post up some details if you do this upgrade.