The 'Oatley' site has a link, (download instructions), to the drive circuit which shows that the circuit runs off 12 volts DC, & is speed adjustable. BUT, it's only suitable to drive the 24 volt AC motor.
Did you have any luck with the stepper motor/driver, links at 'Silicon Chip'? Most are speed adjustable via a pot.
L.
ps. Does the driven threaded rod have a support bearing at the far end? Looks a bit flexible!
pps. My camera tracker is a 'curved rod' type. A 1/4" threaded rod was used, & all I drive it with, is a modified servo with a system of pulleys to give me 1 rpm. It has more than enough torque for this app. Not sure about driving a big t'scope tho!
http://i2.photobucket.com/albums/y7/...35/IMG0002.jpg