sorry for potato pic and caveman drawing, but something like this could be made to fit onto any 60% case with a big enough bezel:
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The only thing I would change is the screws, I'd put those from the bottom and not have them pass trough the top layer.
good call :) cleaner style. it would require a fairly thick top layer but i think 5-6 mm would be doable to get at least 3-4 threads engaged, depending on the pitch of the screws used.
i might actually try to make something like this and have it cut next month when i get paid again.