The bearings are part of the pully. Of it is not you will need yo make sure you have cast pullys with enough metal to machine away for the bearings to fit into. You need roller bearings, not brass bushings. The pullys need to be affixed together, they must be a single unit.
I agree with you, I like to do things myself. If I had to buy the parts I used on mine it would have been cheaper, and better, to have bought a servo motor. I actually did buy one, after I found out the reduction I achieved was not nearly enough.