Len has responded off-line and confirmed (from Jim Lipari's notes) the 9.1/16" dimension for the No.6 outfit ring gear; he was also able to confirm Jamie's data for the Nos 8, 10 and 16 cameras (so my sincere thanks to you both).
I plugged these data into the spreadsheet and tested it against a number of examples I was able to find, both here on the forum and elsewhere. The results are encouraging - in each case the spreadsheet is indicating either the correct gear as supplied with the camera, or the next one up or down (at this stage I'm assuming this is because the actual Rear Nodal Point to Film Plane distance falls between the 'ideal' values for two gears).
I'm still waiting for my No.8 to arrive from the US (it's a long way to Oz!) but when it does I'll test to determine the rear nodal point position (and focal length), then try it at various focussed distances to see whether the spreadsheet values hold true. If anyone else feels inclined to assist in the testing process (!) I'd welcome details of your cameras, lenses and gears to feed into the spreadsheet - the more examples we can compare the better.