OWD,
Between 1901 and 1967 there were more than 5,500 new and used Francottes listed in the VL&D and A&F records. I still have a few years left to index. All of the serial numbers indexed to date are on the Research page of the G&H web site.
Griffin & Howe Research Just click on "Francotte" or any other make that you wish to see.
Most of the Featherweight guns were 26 inch but a fair number were 28 inch. I'm at the point where I'm beginning to measure these statistics and hope to publish findings in the next year or two.