Their GX line is indeed their commercial grade engine. The GC is the dispose-a-motor. That is not to say that it is a low quality engine. I have well in excess of 1000 hours on my CBC
From a maintenance perspective, the major difference is, once the GC wears out, you throw it away. Since the whole engine is probably cheaper than a rebuild kit for a GX of the same HP, no big deal.
The GC has several features of its own. Major among them are weight and noise. The engine is very light weight compared to the GX counterpart. The overhead cam with the timing belt drive is very quiet compared to the cam-in-case design of the GX that uses pushrods. Noise, or lack thereof, was a major consideration, as I originally designed this CBC for use in charging my RV's batteries. Noise in a camp ground isn't very welcome.
The GC is good enough for anything a homeowner, small farmer or even casual businessman (second job, that kind of stuff) will do. It'll probably out-last whatever it's driving.
John
-- John De Armond See my website for my current email address