´Hi Jim - I am certain that you are completely right - this is the lens with option to mount a cone for landscape.
I went into the private home of the seller, a very friendly man who had been collecting all sorts of mechanical instruments and optical devices - including photo related items. I went inside a private museum, and was struck by the respect I had for this guy. The touch of Precision and respect for old mechanics.
He had an old winered Jaguar standing in his garage just beside this huge telescopic device mounted with a 5x7 camera - mounted with an equally huge Dallmeyer lens - this device, made in 1875 would adjust itself to counter the earths rotation when taking long exposures of the stary skies
This guy was a keen jazzplayer, a grandad, a collector and just about the most friendly man I have ever come across - and he sold me this Jamin for peanuts. It´s not long before I´m gonna sit listening to his pinpoint correct and detailed stories about Old Times.
Claus