Easiest way to check is to count the turns. Mark one of the output splines and then turn the input flange and see how many turns it takes to rotate the output one turn. If it's about 4 turns, it's a 3.92, if it turns about 3 1/2 then it's a 3.62. There aren't any other stock ratios available so it should be pretty obvious which one it is. If it's only about 3 turns, I'll take it off your hands.