This link has more info to confirm if your rims are the metric or american bolt pattern:
http://cometkartsales.com/Wheels/
Yep looks like you need an international motormount.
Your kart was probably made before Margay started stamping serial numbers in the right spindle mount. I'd lean the frame up against the wall, and take a pic clearly showing all the frames details, and send it to Margay for ID.
PS: I could be wrong, but I don't think your axle bearing mounts are large enough to install a 40mm diameter axle.
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