Word has reached me from Middletown, PA that Kuppy's Diner is #310. This diner was brought into Middletown in 1938, so this makes the Chautauqua diner a little bit younger.(early 1938 or maybe 1937)
On a side note, the Westfield, NY historian(Marybelle Beigh) has been able to make contact with a gentleman who ran a diner in Sherman, NY, starting after WW2. The short story is that they found a diner stored at a baseball field in Corry, PA, and bought it and brought it up Sherman. The story gets a little strange as the diner was plopped onto tired, which naturally blew as the diner was set on them, so the diner was cut into four pieces and moved in sections to Sherman.
The historian will be meeting shortly with this gentleman to talk about the history of the diner and hopefully pick up a copy of a photograph of the diner, so I look forward to identifying the maker of the diner. Initial research shows the (verified) Mulholland which was in Corry is the front runner. That diner disappeared somewhere between 1943 & 1957(no city directories available in between these years.)