I may be wrong, but it seems to me that if you want the generator to put out 1800 RPM while the control module still sees 2000 RPM, you will need to multiply the frequency by 1.1111..., which is difficult to do
Multiplying by 1.1 will yield an output of 1818 RPM, which is close enough for appliances, but not for clocks. If your clocks running 1% fast is not a problem, then x1.1 should be fine. See the upper scheme in the attached diagram.
It might be better to set the control module to run at 1350 RPM, and use one of the lower schemes in the attached diagram.