Full circle cranks have been used in factory built 2-strokes for many decades,notably on Japanese motorcycles and snowmobiles. Most had 2 large holes punched through the flywheels(Counterweights) on each side of the con rod big end,to lighten that side of the crank to make up for the extra weight of the con-rod and piston assembly. It used to be a practice to "Stuff" these balancing holes with cork and epoxy and similar things to increase the crankcase compression ratio. The Kawasaki Mach 111 motorcycle was a rare example where these balancing holes were plugged by the factory with aluminum plugs.Some skilled hot saw builders have built custom(Steel) full circle cranks for competition saws.They worked well,but were much heavier than stock cranks.
A few (ok,many) years ago I wanted to improve on this,so I designed and had built full circle cranks(With 2mm longer stroke) from titanium,with the balancing holes plugged with magnesium.They featured polished counterweights and knife-edged con-rod.
These cranks were actually a few grams lighter than a stock crank. I built and sold 3 of these,and it was a lot of work!