O.S. Engines 12XZ ABC 12F Slide Engine
Looks like O.S. Engines has a new version of their popular OS 12XZ. The newly designed O.S. 12XZ ABC 12F Slide Engine is setup to max out low to mid speed torque. It has a new crankshaft, new connecting rod, and port improvements.
If you are looking for a new engine, OS is always at the top of my list.