Restoring the outside of the heater box.

[In The Ten Ring]

OK, so I have decided to not remove the flapper from my heater box, apparently that is harder than it should be and I don't want to crack my box flanges.

When this truck was repainted long ago, the painters had never heard of "taping things off" so they painted all sorts of things under the hood that weren't supposed to be repainted. The heater box had a lot of black and yellow overspray on it which I removed with wet sanding.

Now I have what you can see in the pic. What can I do to make it look as original and uniform as possible?