Did you do anything inside the cowl to keep radiant heat from the oil
pan off the cooler? A sheet of .020 AL suspended 1/2" below the pan
might keep quite a bit of heat out of the cooler.

No, I didn't figure there would be a lot of radiant heat from the oil pan.  There should be quite a lot of air flowing from the exit of the oil cooler directly at the oil pan, so I can't imagine the pan heating the cooler core up. 

Tracy Saylor, of  extremely fast RV-6 fame, says he has curved turning
vanes on the *outlet* side of his cylinders to direct the air toward the
exit, rather than letting it hit the bottom of the cowl. Could that idea
be used to both direct the exit air & provide a radiant shield?

My thinking is that there's so little room between the cooler and pan, that I wouldn't want to cut it any closer by installing anything in between.  The pan itself is curved, so I'm hopeful that it allows the air to flow around the pan better than it would if there was a flat shield of some type there.  Could certainly be wrong though.  Any guidance I could give the exit air toward the cowl exit would be a good thing, but I just don't see any way to do it.