250-500cc wr 300 help

have just got my first husky from a bike shop. meant to only have done a 1020 on dash is this in ks or mph? rode it and dumpd oil after first ride and half a serclip and what looks to be part of a shim so have taken motor out and is about to be split what other parts eg piston etc shud be looked at and were best place to get from thanks