2 stroke twins are, as you say, opposed and fire at the same time. But they don't have seperate crank cases, that is why the fire at the same time. Someone once made a two stroke radial with something like 7 or 9 TD .051's. It had a common crankcase but had a blower to pump the fuel air mixture into the engines. Don't remember who, I don't even remember if it went into production.