Much depends on how the engine is installed, and at what mixture the engine is run.
FWIW:
I found cylinder temperatures around 150C (~300F) on most engines when adjusted for peak power. This is in close agreement with NACA technical notes on radial engines.
Power remains almost the same when tweeked to 180C (355F), which is getting quite hot.
Power dropped when adjusting to 120-135C (240-265F). This caused the spark plug to turn quite dark.
All this with non-cowled engines running medium sized props for the engine size.

Head temperatures near the plug boss ran some 15C (25F) higher.

I use an IR meter with open angle of 15 degrees (1:6), so at a distance of 6 cm I have 1 cm diameter measured plane surface.
Correlation to mixture setting is very good, so when setting the needles I now almost exclusively use the IR meter. Then I use the rpm meter to check rpm consistency.