Hex bolts. I used a 9/16" hex bit attached to my impact driver, if I remember correctly. You'll need a couple of shaft extenders to get in there. Didn't budge. Switched to a ratchet with a pipe as a cheater bar, still no dice.
On a second thought with this, just moving this motor will probably only allow the spindles to go with it. The belt requires the upper area to clip into, so make sure you design with that piece in mind as well.