they can't be overdriven
...well, not easily.
If you really need the centerlines concentric, a planetary works.
If you can stand some offset (and if moved sideways the blower is still narrower than the engine), a chain drive can be pretty small and cheap. A pair of #50×2 sprockets need only be 2" thick and 8" diameter, moving the blower CL in a 4" circle (4" L or R, up or down, or 2.8" in both directions etc.), locus at the crank . A 20 + 21 set is 1.05 or .952, 21 + 19 is 1.105 or .905, etc.