Hello Bill - When you see Obama tomorrow, say hello from Wade.
The brown glass 1957 Kodiak was shown in the 1957 Bear Catalog. In late 1957, the identical bow, built on the same frame, was made but using white glass. The White Glass 1957 is exactly what its name suggests, a 1957 Kodiak with White Glass. The 1957 bows have an indented belly.
The sow belly or protruding belly white glass bow was made with two different sight windows. The first one was scalloped at the point were the edge of the limb dips down into the sight window, the later one was noticeably rounded on the edge, somewhat like a 1959 Kodiak. The most common 1958 Kodiak is the rounded sight window.
Unfortunately, the 1958 Catalog, does not show the most common 1958 Kodiak with the rounded sight window. The 1958 Catalog shows two different white glass bows as the 1958. However, the one that is unstrung is the white glass 1957, and the other one that is strung is the 1958 with its sow belly and scalloped sight window.
Over the years, I have pointed this out to numerous experienced collectors, and none of them was aware of these facts.
To answer your question specifically, the white glass 1957 and the non-sowbelly 1958 are the identical bows, just called something different by collectors. Take your pick...
Remember, now, there are still two different sow belly 1958 Kodiaks, scalloped sight window and rounded sight window.
Hope this helps, or at least gives you an additional category of Kodiaks to look for... Wade