I think this is a gy6 157FM. I think this might be one of those odd gy6's.
The most common gy6 is the 157qmj. (most performance parts too)
My buggy came with a 1p57qmj. And because of that "p", it made the bigger performance parts hard to find, or way to expensive. No big bore kit for the 1p57qmj gy6.