Anyone have a really good way of telling a 57 oil bath air cleaner from a 58? Was the bottom part shallower on the 57 than on the 58? My last question is: Was the style used on both 4bbl and 2 bbl?

From the pictures I have it appears that the 1957 base is shallower. The 1957 has a cut=out on the bottom flare on the front of the snout. This was to help clear the upper radiator hose. The 1957 had the decal on either the snout or on the side of the lid. The 1958 has the service instructions and AC name stenciled on the top of the snout.
The 1957 4 Bbl. has a snout only. In 1958 the 2 and 4
bbl. both had snouts.