Colin:
Don't bother. About a decade ago I replaced the mini-lathe drive with this one from McMaster: McMaster-Carr
$143, US made excellence and zero issues. I had gone through several of the OEM drives at that point, they're simply under-engineered.
There's a detailed setup guide that comes with the McMaster drive (it's made by Leeson - in Grafton WI) for how to set the pots - there are six of them for min speed, max speed, accel, decel, torque, and regulation (IR comp).
Works like a dream. Don't worry that it's "non-reversing", use a DPDT switch after the drive to switch the armature polarity on the motor (same as with the OEM drive).
Hope this helps.
-Dave Kowalczyk
Author of TurboCNC --> http://www.dakeng.com