I left the pinion the same (12 on a 56 spur ), according to my calculations it was geared for 47mph, which was too much, with this motor its 38mph, after some more testing i'll probably gear up a tooth. Im just paraniod about cooking the motor again :s
Its super punchy, spins all 4 wheels and wheelies if you stab the throttle at any speed, its good, but then it will feel punchier with the lower gearing.
I butchered my old bigmaxximum and made a heatsink, it was either that or mirror polish the neu