Japanese VMX runs up to 50cc 2 stroke and 100cc 4 stroke class, it is run on a 1 hour endurance format and is the biggest class and total hooter.
Variety of bikes is huge, the whole rainbow from long travel monkey bikes, the predicatble XRs, Peewees and anything else that is considered in the spirit. No big complicated dramas, it is treated as learner and beginner class ... you could probably run later XR if you bought one along.