To date - this project is a good six to nine months old - I've found datasheets for the DC motors (those are 3.175mm shafts, by the way), MOSFETs and MCU used in the wheel but I can't post them because I'm at work right now. I've found that the two motors have 11-tooth helical pinion gears machined out of brass, the steering wheel shaft has a 180-tooth plastic helical gear. The helical gear shape is obviously to prevent the noise backlash makes, and to that end they do work, but the bigger problem is the axial thrust effect; when the motors change direction there's an audible clicking noise as the motor cores shift along their axis (because of the helical gear shape), in some situations in some sims the direction changes rapidly which results in a very irritating rattling sound that never used to happen with the Driving Force Pro's straight gears.

Anyway, this information is useful to people who may wish to build a belt drive conversion since the key thing they need to know is the gear ratio - Unsurprisingly, I'm one of those people (which is how this project started), and if you're planning on using off-the-shelf pulleys you'll need four; 60, 22 and two 10-teeth pulleys. One 10T on the motor shaft (p.s. the cheapest solution is to join the motors together with a shaft coupler, since they're both dual shaft) that drives the 22T as an idler, then a 10T on the same shaft as the 22T that drives the 60T on the steering wheel shaft. That way you'll get the same torque and RPM as stock but much quieter operation. You can adjust the ratios but you'll be trading RPM, torque and also altering your steering lock since the MCU can only count so many encoder pulses before it gives up.

The next step, as far as I'm concerned, is to get my hands on another G27 so I can dissect the PCB. This will take months because I'm still buying things like a bed, dresser and such for my room, so this project is effectively on hold until then. There's only so much I can do by simply looking at the one I've got, after all, and besides I'm hardly going to dissect it because I still use it. Maybe I'll attempt to replicate just the PWM, H-bridge and DC motor part of the circuit, though, and see if I can do something with that.