Here's a Flxette. I don't know if they built any before they went to the fishbowl-style windows (Flxible fishbowls came out after the GMC anti-trust lawsuit). Still a possibliity, but I'm leaning more toward it being someone else's version (Prevost?) Most of my transit time is full-size buses.
The rear end in the original picture had me stumped, the slanting side windows point it toward a post 1961 design. The full size slider next to the driver really looks strange, as does the sedan-type door. Emergency door on left rear also points to early 60's, unless state/provincial regs called for it. I seem to remember something about early 4106's having an emergency door because of some New Jersey regulation. Could even be someone's knock-off, with Flxible or Prevost parts. It'd be interesting to see if there's a builder's plate inside. http://fhtcq.fotopic.net/p26395471.html