I like looking at Thingiverse and I was browsing for ideas. I wanted to enclose the Pi in an enclosure and I would 3d print the enclosure. I found this enclosure and it was perfect. It is for the Pi one and can be found at
http://www.thingiverse.com/thing:608169

I chose it because it had 4 lugs to help with mounting.
I found that my interface board interferes with it so I cut a small slot which is even better. Now the HDMI socket is not taking all the strain.

Now for mounting I measured the distance between the holes and it appeared that it was 75mm in each direction.

I designed 2 braces that both have 4 holes but one has them all inline and the other has 2 of them offset.