Hi Alex, thanks for chipping in.
The scope is for visual only and will be on a dob mount and clamshell ring similar to the one shown in this picture
http://astrogoods.com/007a.jpg
I re-ran the newt calculations using a 12" OD tube and a lower profile focuser and I think I can use a smaller 1.83" secondary while still maintaining at least 0.5" 100% illumination diameter.