Good Morning!
I've got an idea: Unless they've "yellowed" in lieu of "mellowed", why not leave them in their natural state?
I realize that I'm showing my age here, but to me there's nothing that screams "vintage" more than an aged kit that's both functionally and cosmetically sound!
Now, if the original wrap's got scuffs, chips, tears, etc., that's another story. But an over-all "natural" fade through the years on all the drums gives the kit "character" IMHO.
As a comparison, there's NOTHING "natural" about the 60 year-old co-worker who walks into the office one morning with shiny, "shoe-polish" black hair only to announce that he just removed "a few" of the gray hairs. Sure he did!DOH
Good luck in your project, whatever you decide to do! How 'bout posting some before and after pics?