Looking at images online, it looks like that combo unit has a mounting bracket built into it. Its not going to line up with anything in the case, but its there.
One option is to get a drill, make some holes, buy some short bolts+nuts and use that to mount the unit to whatever surface you want really. The dead simplest option though would be to just put it on top of that removable drive cage, once everything is set the tubing wont let it move much.