I have a pair of pre-Katahdin Chippewa engineer boots, which I think probably fit the same as the Katahdins (pic of them here with Oak Street and Vibergs). The closest Viberg last is the 2045, which they call a "modified Munson last." It has the same shape more or less. Fitwise, I found that last to be proportionally longer and slightly more narrow than the Chippewa Munson last. A size 10 Chippewa fits me perfectly, with a bit of extra room for an insole; but the size 10 Viberg was longer and, with an insole, too tight in the vamp. I've also worn the 310 and the 110 in Viberg. Those are very different overall than the chippewa Munson. The 310 feels a half size longer to me, but right on in width; the 110 is a bit wider in the vamp, and very wide in the heel.
Chippewa engineers / Oak Street Boots / Viberg Service 310s
Ok thanks for you input ! I guess I'll just order the same size as my LL Katahdin and hope for the best?!