Soft mounts on any of these small singles - is a no no -
The problem is not so much the inherant out of balance of a bigger single - but-- is simply the kick of each firing and the reaction.
Th twins the same size - if they have the same powe - will also kick -as either engine fires ONCE each rev - ( the twin fires both cyls at the same time.)
The engine ignition system used on a lot of singles - has a retard which softens the blow at lower rpms but if anybody has a mount which is very light and eliminates this power pulse - I would like to see it - (I have seen the ones currently on the market and the European shock absorber ones plus others )
Bottom line - mount solidly - to a solid front end on the model -make sure the fuselage does not flex - use a stiff , balanced prop and go fly -