How much modding would you think is necessary to accomodate 6 GPUs? It's ATX compatible, if the front bays are removable (looks like they should be) one can just stick 120mm fans in there. I suppose the only thing would be a transversal bar to fix the GPUs at the front (and maybe a second underneath to support them on the risers)?
That looks a lot like the Rosewill case. There is a mining version of it:
I use the old 4U Rosewill cases for some of my miners along with custom aluminum frame to support the GPUs and fans (front exhaust). I will try to dig up a link for the guy who makes them.
EDIT: Here is that link for the drop in bracket for the Rosewill case: