Reuben Henry Wilbur was born in 1825, so I doubt he was Betsey's father. But Reuben Wilbur's Civil War papers such as his Muster-In Roll, Muster Out Roll, as well as many other papers of his including his G.A.R. booklets were in our Davis & Cunningham family trunk.
Then there are the two excellent drawings: #1 drawing is captioned, "Camp of 1st Brigade, Genl Sigel's division, on Cedar Creek, Va. Drawn by James AllenCo. "I" 102d N. Y. Vols". This was excellently drawn and with such extreme detail. It's great!
#2 drawing is captioned, "Hd. Qrts. Ellis Ford". On the back hand written in ink, "Our Head quarters at Ellis Ford, on the Rappahannock, in Aug. 1863. -- after the battle of Gettysburg". I believe this also was drawn by James Allen, as the overall look of it is the same.
#3 drawing is a very rough drawing of a map showing the army's positions. Though it is a rough drawing possibly done in a hurry, I believe it too may have been done by James Allen.
Do you happen to know if your James Allen had a talent for drawing things with such excellent precision? All I have on James Allen is his name on the one drawing, and possibly the others are his as well. If you have any possible further information, please let me know. You are right about coincidences to some degree.
But why they are in our family trunk is unbeknownst to me. I've never heard of an "Allen" line connected to us. So the search continues! I look forward to hearing from you.