In TimBle's example of a "180 degree V" engine there is no way it could be made to scavenge as a two cycle engine. Been involved with many opposed cylinder engines, if two rods share a journal on the crankshaft it must scavenge four cycle, must have four or more cylinders, and it's termed as an opposed cylinder engine. A boxer design can be made with only two cylinders and can be made to scavenge two or four cycle no matter how many cylinders are used.

Two cycle engines can be made with shared crankshaft journals but they are more of a four cycle design forced to operate in a two cycle mode. They require a separate pressurized oil system, oil sump, and pressurized air intake. I don't know of any that don't also use overhead valving for exhaust at least and some form of fuel injection, none use gasoline for fuel.

A true boxer engine uses one crankshaft journal per cylinder, many are made without counter weights being necessary for balance as are many opposed cylinder engines. There should be very little rocking couple in a well made boxer engine as all forces should counter act each other. I have several model airplane boxer twins some have counter weighted crankshafts and some do not. The ones with counter weights do run a bit smoother throughout all RPM ranges but the ones without counter weights are acceptable.