Dennise you are absolutly right. On 12 engines from factory with stock P/S sets it is pretty good balanced.
You have mentioned about soft mounting. I did use those on tether hydros and I can tell is very important ( 60 size) that were si center of rubber mounting located-over the center line of crank, on the line or under. In those points it was realy important pretty good ballancing-the vebration point was changing power, blew glow plugs, blew pistons,blew cranckshafts etc.
One more thing about different balanging in hobby-it is control line FAI speed and combats-motor is on horizontal position with head out of circle. That one is another b... ch to work with. There centrifugal forces changing whole story. It was a lot of tryes to put motor vertical with head up, but aerodynamic was bad.
Edward