Yes Big Bore it' s not possible to shift the stock gear with a stock motor on 660'.
Engage lower, around 3600-3800 with moderate cam angle, 42-43* and shit to 38-37* and try to keep the engine RPM betwin 8100-8250 max.
Also hold up the front suspension for dont have to much transfert and lower the sled(front and back)
Run stock primary and try a little bigger roller.
Last year with a 750, stock clutch, stock engine, stock gear(94) 800 stock pipe, 800 CDI and safe jettinf I ran 182KM/H on 2500feets. Verry good for old stock sled.