JB Weld is sandable and paintable (although I don't know how well it would take other coatings), and with proper prep of the metal I can't imagine it popping out of the lettering.
I think you make a good point about other coatings.
A difference in texture may show through.
I'm going to ask my smith about that. I am looking for some
education before I ask him and I'm getting that. Thank you.