Joe,
There is a company "www.microkinetics.com" that makes a retrofit kit for your mill that uses 2-470 and 1- 350 oz stepppers and 2 to 1 pulley reduction for X and Y axis.
They charge about $4,300. for the kit.
There are several people on the CNCzone that have made the stepper mounts etc...
Take a look at these images, they will give you some ideas to start with.
The last set of images is interesting also.
http://pashupatina.com/gen2/album/ http://ivan.pashupatina.com/cnc/cnc_2/images/ http://tinyurl.com/5d6yh6