When dealing with ratios, the math is always driven teeth ÷ drive teeth (or driven diameter ÷ drive diameter if using pulleys). Work out the individual ratios then multiply them (2.68x3.45=9.246) so you may need a steeper sprocket ratio than you think. Also, CVT's usually give very little overdrive, something to the tune of 0.8 : 1. My guess is Polaris used the steep reduction to allow full primary clutch engagement at low traveling speeds, to prevent slippage from prematurely wearing out the belt.
1985 Tri-Z 250
1985 ATC250R