Mine is a Lynch Rd hemi car with a 70X on the trunk lid. The broadcast sheet shows a body colored spare as well as wheels and dog dish caps and F70 red line tires. Now for another thought. Back in the day the owners manual shows how to rotate the tires which included the spare so if you had poverty caps they didn't want a black wheel in the rotation it would be body color excluding black cars . The full wheel cover cars got the black spare along with A12 of coarse.
So yours seems to lead us to believe X is not necessarily a black spare wheel, and it is not blackwall tires either.
And yet we have other examples of "Red" and (now, above) we have a "W".
I guess I'm back to square one: No idea
