I feel your pain!! I spent years getting my CHTs below 400F, what I have now is mostly cut off air dams as my 1-2 CHTs are not much cooler than the rear 2, I put a deflector over 3-4 to move more air over them to 5-6, and I even put a deflector behind 6 to force the air down into the rear. In the end, a good friend and mentor suggested I use more flaps on takeoff- Make that where you should focus next steps on. My temps go above 400, around 420F on takeoff but well within the lycoming 435F "normal" for takeoff range. Cruise however is at 55% 50F or so LOP around 370F the hottest and 340's coolest (Summer in SoCal). Since I spend 90% of my time cruising that is where my efforts went and I am happy with a 30F-40F difference between cylinders.
You have to get the injectors tuned to .5 or better, If I ran ROP my CHT's would be significantly higher too, get it tuned and those temps will go down.
Keep us updated on your progress!