It sounds like their standard ATX case.
Their standard case used a standard ATX board with standard ATX port locations. Boards they used with ports missing had those ports covered with a white sticker, which you can trim out to gain access to the covered port holes.
The problems are:
1.) MOST new boards no longer use standard port locations. Instead, most newer boards include a non-standard backplate made to fit a standard backplate hole. Gateways cases don't have a removable backplate, so you need a board with standard port layout instead. Newegg has pictures of their boards so you can decide for yourself which boards do.
2.) The power supply isn't a standard size, so replacing it can be difficult. A standard size power supply will fit if you cut the hole in the back of the case larger.
3.) Some G6 towers used a 1-piece front panel header. Yours is new enough that it probably does. You'll want to pick up some dongle ends from an old case in order to switch them. Yes, you can switch them.
If you would like to see a G6 style tower modified with a removable backplate, etc, take a look at the Opus case review from Sysopt, where a G6 tower is used as a basis for comparison.
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