Atwood makes several models that can be used to replace the GC6AA7. Generally speaking, nearly all the 6 gallon models have identical specs for the cut-out size and can be used to replace each other. There may be small differences in gas and water line hook-ups and differences in electrical connections if you replace a pilot model with a DSI type or something like that. I'm not familiar with either of the models you mention, so am not sure what type they are, e.g. DSI gas, pilot gas, DSI gas + electric, etc.
You can review many of them at Ductec - Atwood heaters Their web pages identify what older models the current models will replace.