Could these be the transitional knobs referred to in the
F-2B FAQ? There, Mica writes that ...for a few hundred units, the knobs were all-aluminum with two set-screws and could be found in both black and natural aluminum colors (both colors were anodized). The supplier was Alco.
If so, isn't it interesting that two F-2Bs with transitional knobs went on sale at the same time?