Bull,
The 988 had a wide ratio g'box w a rather large gap between 1st & 2nd, which wasn't helped by very tall gearing & the 'asmatic' pipe. Std c'shaft sproket was 18 or 19T.
However top 4 gears were much closer spaced. I suggest you gear it down considerably & use (mostly) the top 4 gears on the track. Probably need a bigger carb too, & obviously a better pipe.