I suppose the extra paint on the radiator could be adversely affecting things. I do know from past experience with my rex, that the process you use when refilling the system after rebuild can directly affect things. I found that using the procedure listed below (which is from another member post here...sorry, if I could remember whos' I'd give you credit!) made all the difference in the temperature on my car...maybe it will help?
Put a short piece of clear tubing over the air bleed screw so that the tube is higher than the radiator cap. Crack open the bleeder screw until the tubing fills with fluid and watch for bubbles coming out of the tubing. Leave the bleeder screw open, as the tubing will prevent you from leaking coolant.... it will seek it's own level. Jack up the right front corner slightly to tilt the head up towards the bleeder screw. Set your heater on full heat. This will open the coolant lines to the heater core.
Remove the cap and fill the radiator to just below the seat (where the base of the cap seals). Fill your overflow so that it is between the MIN and MAX lines on the bottle. Gently give all of the hoses a gentle squeeze to 'burp' the air out of the system. Top up as needed. Now start the engine with the cap open and the bleeder open. Continue to squeeze the hoses with the engine running until you don't see any more air burp out the radiator, or see any air bubbles coming out the air bleed. After about 60-90 seconds, close the bleeder screw and replace the cap. Allow the warm up fully or take it for a short 5 minute drive around the block until the fan kicks on at least twice. Park the car and allow it to cool fully. When completely cold to the touch, remove the cap and give the hoses a couple of squeezes to confirm the air is removed. Top up the radiator (if needed) and top up the overflow (again if needed).
Top hose hot/bottom hose cold = clogged rad.
Engine overheating/top hose cold = faulty thermostat.
Skip