You have to have a spot for a keyway in the drive shaft. That way the drive wheel and the pulley can stay on it.
I just got the plans and have an order in to pick up Friday from a local metal/fabrication shop. It should be less than $100 for enough metal to build everything with all attachments (flat platen, slack, a couple reg. tool arms, a rotating arm from jtknives plans).
My new motor will be around $200. I can't find a good used one.
I will prob. spend less than $800 but will end up with a totally awesome grinder. I could cut some cost and lose functionality but I want to do it up right since I'm investing the money anyways.