It's not your "average" B12 motor. He's got a 1216 kit with a ported head, bigger valves, GSXR cams, 38mm Mikuni smoothbores & Holeshot full-system header/can. It's certainly not an unrealistic claim for crankshaft HP and may even be pretty close for rear wheel HP. Dale got 148.2 rear wheel HP with a similar set-up (Dale's was short the bigger valves and smoothbore carbs).