My Sheehan/Lyons family is from Brosna & Castleisland, Co Kerry. It appears that the Lyons were Lyne(s) in the Irish Civil Reg'n. I suspect that my Lyons were originally from Co Cork--but when 'orininally' is I dont know!!
The Mahoney name is also closely linked to Sheehans of Brosna.
Much of my info in on-line in various posts & I'm guessing you've seen this already--Daniel Michael Sheehan b. 1876, son of Mortimer; Johanna Lyons (wife of Daniel) was dau of John Lyons & Johanna Sullivan (dau of Timothy o'Sullivan & Frances McKnightly or Knightley).
A lot of immigrants from Brosna & Knocknagaschal came to Mass & Vermont first & scattered from there, many working on the RR.
Please keep me posted on your search--I cant help but think there is a connection somewhere!! I'll be glad to share any info you would like
Good hunting!
Molly