small 1"ish pulley on the motor, large 10"ish pulley on the grain mill to lower the rpms.
There are a bunch of threads on motorizing grain mills that will help you out.
I'm actually motorizing my monster mill mm2.0 tomorrow. I'm using a 3/4 hp motor from a garage door opener. I got a 1.5" pulley and a 12" pulley with a 45" 3L v-belt from grainger.com