I have three aerial lenses: two Kodak Aero-Ektar and one that's not an Aero-Ektar (looks like 6" Metrogon but patent # is for Zeiss Topogon, a slightly different design).

The 12" A-E is in a barrel (conversion probably); I hope spacing is correct.

The 24" is in its shutter still; I removed the spring and am replacing it with a very small tiny variable mechanically isolated motor and belt drive.

These two have front and rear focal lengths engraved on them.

The 6" Metro/Topo is undergoing the same motorization treatment. I think the front and rear f.l. are on this also, but not sure.

Question 1: Is the rear f.l. info useful for determining spacing for a box camera?

Question 2: The Topogon may be a little wider angle than the Metrogon if they followed the patent designs literally (100 degree vs. 90 degree).

The lens designs discuss three options including 4 or 5 elements and a planar (0.002 millidiopter max) element as an option. (A planar element shifts focal length by approx. 1/3 it's thickness for typical glass, so it does have some effect in the lens design) The 'center spot' filter used with these may be the planar element also, in addition to evening out the corners.

If this covers 8x10 as the Metrogon does (it was made for 9" x 9"), and I use it for 4x5 or 5x7, I am thinking I might be able to pull the yellow or red filter and use it for color (coverage for smaller format hopefully isn't as dark in the corners with the filter removed).

Has anyone heard of a Metrogon-type lens used for color with no filter?

The 6" lens is not a radioactive one with discoloring glass, so that's not a concern.