G'day Rob,
you could what I did. I get a secondhand EQ6 drive-controller-steppers
from who upgraded to a go-to. I payed $60. The EQ6 has a 180:1 worm, yours is a 144. Then ask
http://projects.gbdt.com.au/eq6-1/
Darren for a PIC upgrade for about U$20 with pcb and reprogram for a new ratio (you can do that with a pc and parallel port).
As a bonus you have micro-stepping, guide port and go-to
(slow) with a planetary software. Check it out!
Best Regards,
Mick.