As Julian said, sizing is about the same as PNW boots in my experience.
This shop has some beauties for sale that all appear to have been made before the change in ownership:
https://cwoodcockandco.com/shop/ols/search?keywords=russell moccasin&sortOption=descend_by_match
Sizing is pretty limited sadly. Consider it your lucky day if you find your size there.
Here's a quick snap of my walking shoes (double vamp) and Art Carter chukkas (triple vamp):