For buggies bigger is not better.. Look at something like a Werks B2, B5, or B6.. Top end goes up in about that order...

Argus, Alpha, and Go also make great buggy engines.. I think there are some distributors in NZ.. Dude called Grizz I think from another forum.. All those engines are more for racing though.. Need a good pipe and clutch, and starterbox with batteries...