balancers?

I am only aware of the Romec SFI approved ones and don't think they are much smaller, maybe a bit over 6". But check them out; pricey. BTW, these are dampers, not external balancers, so are neutral balanced. To make it work effectively as a harmonic damper with smaller diameter, the unit has to be a lot thicker/deeper to provide the same damping.... or the outer ring needs to made of lead LOL