Yes, because of the way that they work, you can only use castor oil. Apparently it doesn't mix with the fuel, so stays stuck inside the engine to do its work.
He said its producing 110 hp and 720 lbft of torque @ 1100 RPM. (Not 100% sure of the units for torque, could be Nm, either way, its a ridiculously huge amount)
The frame that it is attached to has a torque sensor attached. Other than that, I don't think there's a dyno that would handle it (especially given that it needs to be hand-swung to start, and for that you need the propeller attached.