Sancho,
To give you a good look, I've posted a picture of both the C730 and G730. Note the face plates, dial, knobs and chassis are identical, but they almost always have a different grill cloth design. I've often suspected the G730 could be a more expensive radio, as many of these sets have real wood cabinets, but both of these examples have a veneer finish.
The only differences inside is the G730 has a steel brace that runs from the chassis to the top of the cabinet to offer some additional rigidity, while the C730 features a tin heat shield over the FM sector (to the right, looking at the radio) where the tubes bunch together. Properly serviced and looked after, they return exceptional sound and reception and polish up like nice furniture should. I really love these sets! These are the radios that sparked my interest in antique radio and collecting. A handsome, durable all-day user.