Mechanism Automation

I am putting together a rather complex gearbox, and have done all of the math to get the correct paramaters for the entire assembly.

Many of my parts automatically regen upon changing the paramaters, but one thing I seem to have to change every time I change my gear ratio is the gear ratio in my mechanism link. Anyone have any ides on how to enter reduction ratios, certain pitch diameters, etc. into a mechanism link?

Thanks