Give Russell Karting a call or an email. Jim Jr posted in 2010 “I like 16.25-16.5 for road racing. 16.0-16.25 for sprint racing.” For RR that works out to be 412.75mm to 419.1mm.
P.S. I might still have a flex cutting jig if you need it.
LAD Specialties / tony kart / rotax / kt100