Here's the link to George's article (#4 under what else at the end is the only info on the grey faces):
http://www.oldbaseball.com/refs/5253printing.html
honestly, I don't consider this much of a variation. I have a few that are arguably the grey faces but the differences are so subtle that I do not consider them true variations (and both Boone and Kretlow have much bigger variations). I think the Crandall face variation is more obvious and distinct ... and that one is hard to spot too.
I don't know exactly what was included in the master set as variations for the black backs, but the Boone, Kretlow and Wehmeier are undoubtedly three of them (in addition to page/sain). Probably the Parnell as well.
Cheers,
Patrick