This is the case for the NAVIO+ autopilot that I have made. In the pictures you can see that it is almost a perfect fit. In the uploaded version you can see the names of some of the input and output port that I did not print in my case, but just give it a try and print it.
A few minor changes have been made to the case to ensure a better fit. Also, ventilation slots were added.
To put it together just use the 11mm spacers of the navio, but you will need at least 8 M2.5X8 allen screw/bolts.