Hi Warren,
There are already some off the shelf motors, a simple on is the Celstron and just modify a bracket to suit.
http://www.celestron.com/c3/product....=44&ProdID=518
If I was to go for this motor again I would change the control to a 10 turn similar to what I have done on my current EQ3. This is the most common.
I used to have one but I raided it early and since then I have placed another motor.
So far I only go 55mm and working my way up to about 300 or 600mm FL before considering getting a guided or high end mount.