Need X (long) axis pinion gear specs for PRSAlpha

I need a pair of pinion gears to match those on the long (X) axis of my PRSAlpha, but with a 1/4" bore instead of whatever the stock ones have. I'm constructing a second, lightweight gantry to carry some experimental tools, and I want to use the existing drive system (V-wheel track, rack & pinion drive) on that axis (the stock gantry will, of course, be parked out of the way while mine is in use). My new gantry uses much smaller NEMA 23 steppers that have 1/4" shafts., and all of the motors (X, Y, and Z) will be run by a simple, independent controller instead of the ShopBot's controller. The problem is, I know next to nothing about gears, and despite attempts to measure the existing ones I have had no luck finding any that mesh smoothly with the ShopBot's gear rack.

So, can anyone give me the specs I need to buy matching gears? If I'm understanding correctly, I need to know the module, pressure angle, and pitch, but the number of teeth will depend on my setup and torque requirements (to be determined).

Any suggestions will be very much appreciated, as I have been struggling with this for a while. Thanks!

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