[AdamHeard]

I'm pretty sure the FP gears are .8 Mod. (Based on my recollection that stock FP pinions are 31.75 DP, aka ~32 DP. Knowing DP = 25.4/Mod you can solve and get .8 Mod)

Pitch Diameter (mm) is Mod x Toothcount.

So, for the 72T gear.

PD (mm) = 72 * .8 = 57.6 mm

PD (in) = 57.6 mm x (1 in / 25.4 mm) = 2.268 in (although I imagine it'd be more accurate to just enter the metric units into SW)

I know you already know how to get C-C distances, so that should cover it for you.