I was watching Diners, Drive-Ins and Dives on the Food Channel last night. They showed a Mexican restaurant in Chicago (I think) doing the meat cuts and mounting for the al pastor tacos. You might be able to get the episode on the Internet or Netflix.
In looking at your spit, I doubt that you will be able to use direct drive in a vertical position; however you should be able to use belts, chains, or gears to drive a vertical shaft with the motor mounted separately. I think the constant weight of the loaded shaft would burn the motor up too fast. A small electric motor should have the torque to turn a vertical shaft but I don't think you should put the weight load on the bearings.