Cowl flaps
You asked about cowl flaps- these are really nice-http://antisplataero.com/EZ_Cool_Flap.html
I would balance the jets first, as many recommended, it will make for a better leaning engine and with that will come the cooler CHT's. Airflow will work with you over the phone, they are a good group of folks. I did mine on my own and get about .1-.3 usually, My temps go down below 400F quickly when I pull back and lean, if I dont lean temps dont drop much.
#2 cut that dam a little more, #5, my #3 was the coolest so I took the advice of my mentor and put a dam over the #3, that brought my temps lower for #5 and alittle hotter for #3 and pretty close from coolest to hottest- range about 40F.
Pascal