My combiner is a 1:1 gear ratio. i bought some of the metel gears from ric at garden trucking the rest i bought from mcmater car and drilled them out. it was a pain trying to find the gears in all metel. you can use pinon gears and drill them out as well.
the biggest problem is the buhler motor shaft is 4mm if i remember right,
and its hard to find gears with that bore so i bought some 4mm drill bits and drilled them out. its a hodpoge of differant gears but it works.