The main difference is that the GX-series engines are commercial duty while the GC160 is residential duty. Other differences:

• GX-series engines have low-oil shut-offs, which prevent damage to the engine.The GC160 engine has an aluminum bore where the GX-series have cast iron bores, giving the Honda GX- engines a longer life. GX-series have fuel-shutoff valve so that if they are run infrequently you can run the fuel out, which is easier on the carburetor. GX-series have on/off switch where the GC-series have on/off combined into the throttle control. You'll find a lot of metal on the GX-series and plastic on the GC. For example, the gas tank on the GC is plastic; on the GX-series it’s steel.
• A bonus with the GX-series engines is that they are available with an integral power supply unit allowing the Point of Entry Safety Light option. Because the POE Safety Light is wired directly to an alternator in the engine, it is not available on the GC160 or the Kohler engines, or as an add-on to existing fans.

Below: Honda GC-series engine