Thank you for the follow-up that's extremely helpful in picking a cylinder from a dozen or so choices. After looking at the dimensions on Robart's page for their air cylinders I see that the so called "3/8" versions actually measure 1/2" on the O.D. so we may still be talking about the same one ! I think you have the model 165M
I have found a Robart that offers 1.18" of travel (I can get them quickly from Tower) and I will first try with those and by simply moving the horn very slightly inboard to allow a sufficient travel. This will be very close to your set-up and hopefully with the correct tweaks will work-out !
Thanks again,
GM