that number denotes the sx engine from 97. not surprising. could be an engine swap or someone simply longtracked the sx chassis and called it a mtn max. not much difference between the two except track and skid. yours having the aftermarket tunnel, anything is possible. measure your ski stance.
seems like around 14 bolts originally in 97, but its been awhile. 6 more were added for 98 and up along with a different crank bearing configuration.i think the newer crankcase castings had "ears" or "lobes" evident under the intakes and exhaust.