The problem with updraft cooling---whether it is from armpits or a NACA---is that the cooling is worse than you think. CHT numbers are published for the bayonette fittings with downdraft cooling. There is quite a bit of temperature difference between the hot and cool side of the cylinder. There are some CP articles that deal with "converting" your CHT readings---but they are really only a guess.
When I had my Longez, I was more interested in cooling than speed (after trashing my first engine). I used 4 inch diameter pressure plenums with a large exit. I was around 350-375 on the bayonettes (good temps) with 180 on the oil. These same readings for updraft would be a little on the hot side.
Baffling must be tight---no leaks. Check your baffling at night---shine a light up underneath and see where the light leaks out. Inter cylinder baffles are important. Downdraft baffling is much easier to seal than updraft baffling (in downdraft baffling, you don't have to baffle around the starter and alternator, nor any of the other odd shapes on the back of the engine.
On the Cozy, you build a ramp on the entrance of the NACA to divert air to the front two cylinders. You build the ramp extra long----take the plane for a test flight at typical cruise alt and speed and monitor the temps. If everything is ok, the front two cylinders will be the coldest. You then start carving away the ramp until all the cylinders are of equal temp for those conditions. In the end, if your cylinder temps are equal---but are still too hot---then you have too many air leaks---or the mixture set up incorrect---or you may have an inlet/exit problem where air is spilling before it gets to the NACA (use oil to check for this).
