This is a case for the "Minigun" arcade supergun created by Frank_fjs and published on the arcade-projects.com forums. This is designed and tested to fit the v1.7 "advanced" edition. I am also providing an untested version for the "standard edition." You can choose between the version with embedded text, or without text, whichever you prefer and suits your needs.
Make sure you print this with a well calibrated printer to ensure volumetric accuracy, the tolerances are pretty tight.
To print, I use prefer PETG, but this should work fine in PLA. I use a 0.2mm layer height, 5 bottom and 5 top layers, so that the shell is completely solid, and 4 perimeters so that all the walls are as well. 20% infill for the rest.
To assemble, you need 2 x 20mm M3 screws, 2 x 12mm M3 screws and 4 x M3 nuts. You might need to replace the 12mm with 14mm depending on the JAMMA connector on your board. The nuts might require some work to fit in the first time, screw down with the nut carefully aligned and tighten it until it is completely set. Don't worry if you don't have the screws and nuts handy, the fit between both parts is good enough to stay in place without them.
I use a 12mm piece of 3mm diameter lightpipe for the power LED.