Quick Change gear set 23/25 10-spline in Speedway Motors box

The gears are in a Speedway motors box with a code of 916-81204. The gears are ten splined. The smaller gear has 23 teeth. The larger one has 25 teeth. The outside of the box is marked "5.28". The gears are stamped C528447-1H6 and C528447-2H6.