Since the gear ratios are different in the 300 fourtrax. I was wondering if you were able to chage out the gears in either the front or rear differential to allow running of the same size tires front and back.

 

A lot of people do use the same OD tyres front and back. It will wind the transmission a bit on asphalt. Your chance of getting alternative ratios for the diffs would be slim. You can't use the same width of tyres anyway as it won't steer on fat front tyres.

 

Probably no chance, but these units (TRX300FW, '88-'00) were VERY popular for mudding. I have had mine for many years, and I bought aftermarket Chinese ring and pinion for the rear final drive, but they were stock size, and still 200 clams.