Sturmey Archer S2C/S2

Starting to look at an alternative fixed rear for my S2C-equiped Moulton. Moulton list the gear ratios for the bike as 51" (direct) and 70" - but I can't get a 44x17t on 1 3/8" 20"-wheel to come out at 51". Sheldon gives it as 47.7", Gear Inchy as 47.4" and CTC's spreadsheet as 49". Am I missing something??

Anyhoo, I'm looking for mid/upper-sixty-something gear inches. So go up 4-teeth on the chainring and down 4-teeth on the sprocket to keep same chain length: 48x13t gives a nice useable 68". (It would be better just to go down on the rear sprocket but 44x12 to give 67" would see the wheel out of the back of the dropouts with an inch-and-a-quarter more chain). So it seems I need to find a 104-PCD 4-arm 48t chainring...

I was wondering if you'd be interested in selling the one off your moulton or perhaps the other one you mentioned before off jammy (if you still have it) Cheerz! Mike