So i need a new piston for my 1983 atc250r. It has a big bore kit on it but not sure how big. I measured the old piston with my calipers (which are in standard) and converted to metric it reads about 75.4062mm. Im need help finding a replacement piston. What is the cc? Wiseco sizes there piston by .020, .040, .060 over so what do i need?