Keep in mind that the only correct, safe way to do painted numerals is OVER the clearcoat. The type of paint used for sign lettering will run and have issues if clear coated. You could have a vinyl mask "negative" made of the number so that the number could be spray painted on the roundel in the urethane Hi-Tech uses and THEN it could be clear coated.
My suggestion is to have an old time sign painter do the numerals over the roundels clear if you really want paint. BTW, don't EVER clear over a vinyl decal.....you WILL regret it!!!!