If you bolted stand-offs onto the boards, then all you'd need to do is drill the holes in the right place in the case, and bolt everything down. The cases themselves don't have to be tapped. As for the input/output jack holes, again just drill a simple hole, and use a nibbing tool to cut the right shape out.
That how things are usually done at work, for one-offs. Although we do use a drill press for the holes, just because it's there. There's no reason that placing 4 dimples and then going at it with a hand drill wouldn't work.
