Dammit I just got an error after writing a long post:( Anyways- here is a quote regarding measurements of the base which attaches to G940 "To attach the tube and the base, can be used aluminum tube of 19 mm and 1.5 mm wall or 18 mm and 1 mm wall(19-3=16mm or 18-2=16mm). I can set with two bolts.
The stick fits perfectly into the aluminum tube 16 mm, just needs a through bolt to secure" (full thread here: http://forums.eagle.ru/showthread.php?p=1386793#post1386793 ).
The reason why I thought it'd be good idea to release just a grip with a stick is FFB really is the best option for helicopters and I cannot imagine giving it up even for such a great project as Yours. If Your grip has double stage trigger for ics\ radio, hat for hoist etc, maybe people would be interested in getting such grip with a simple usb plugin for connection with pc? Please let me know what You think, I would ask my friends over another helicopter sim forum and I'd probably get few more people to order it for sure.