I went to the airfield pretty early, and took the plane out for a few circuits (before it got too damned bumpy to be having any fun). So, the new engine seems to run just fine, and I didn't see any CHTs above 375F, where the old engine was getting well above 400F on take-off. Of course, it was cooler, so that'd make a difference :o) I set the trigger for the warning light to 435F (Rotax say 480F is the absolute red line), and I'll keep an eye on it for a bit.
In the early evening, I went back to the airfield and did another 80 minutes of circuits in >90F, and the CHT never went above 425F. I think we'll call that fixed :o)