So your idle varies a little with temp A 383 engine at 205 is NOT OVERHEATING. I really believe this is a case of a cam that a bit radical compared to stock. Either live with it or change it back to stock. On a 69 383 road runner I run the timing at 42 total with at least 15 initial or more No vacuum with stock cam exhaust and 3.55s it will run 14.3 at 97 on street tires and a high 80 day. Enjoy the car and quit worrying aboiut nothing