xeanus:
Itsid's reply has a really good point about the difference between 2-cycle and 4-cycle racekart frames.
The big problem with many 2-cycle frames is the angled rear crossmember not leaving enough clearance for a sprocket located inboard of the 3rd axle bearing, you'r pics don't show this crossmember...
You really need to post another pic of the back of your kart, so we can give you better advice. We need to see a pic without the engine or motor mount, and from the same angle as this pic I've posted here, so we can see the frames rear crossmember to axle clearance, and also see the locations of your seat mounting struts.
You need to post a pic of your kart from this angle:
The rear crossmember of this racekart leaves plenty of room to instal a sprocket inboard of the 3rd axle bearing, we need to know how many inches of clearance your kart has in that location...