You could be right Jon but a 180 is what I have. It is considered a "normal" lens for the 6x17 so I figure to give it a try. My design will allow for changing to a different lens and lens holder and after using the 180 I may well be looking for something a bit shorter. I'll be making the camera body shallow enough to allow me to mount something down to a 90mm. Longer lenses just need a longer mounting box to allow for their longer flange focal distance.
I'm sorta thinking about how I might incorporate some kind of dark slide to allow for changing lenses mid roll but I'm thinking its starting to get out of hand here and a roll is what, four frames? Probably not worth the effort and complication.