Perch,
I've built (4) Vincents to date. (3) were from the old Golden Age Arms Co. Jim Johnston was the original owner. His kits were taken from an original in his own collection.
With his kits, he sends a small booklet with multiple pictures of the original gun.
The Ohio guns were mostly percussion, pointed tang, double finger grips on the trigger guard. Mounted in brass with German silver inlays on the cheek, and on the forearm barrel pins. The barrel pin inlays were a double scroll type attributed to Vincent rifles only. The cheek inlay a 4 pinted star with a square in the middle.
As far as the under rib, at the end of the forestock is a poured pewter nose cap that wraps around the under rib, which is screwed to or soldered to the barrel and terminates at the muzzle with a tapered or rounded off end almost flush with the muzzle.
I'm not sure if any of these books are available as Golden Age is out of business, but would be great to have if you could find one.
Hope this helps.... good luck