I have an 01 Sprint with Airsal 64cc kit. I used the stock head but reshaped it for the kit. I polished the ports and bevelled the port edges before assembling, and gapped the rings. I opened up the exhaust port to match my techno bullet pipe. I also opened up and semi-smoothed the intake all the way to the carb. Stock 14/12 with a #69 jet, and pantyhose filter over a 1.5" ABS pipe about a foot long.
With 27/20 gearing, the Sprint will go 42-43 most of the time, and occasionally climbs to 46-47.