Just want to share my OpenDive design with you.
The original design is here : http://www.thingiverse.com/thing:96878
I took some ideas from the Croccy22 design : http://www.thingiverse.com/thing:93460
My version :
The lens holder has teeth. It can't rotate, so it's perfectly guided.
Each movement on the left or right moves the lens by 1.5mm steps, and you can move freely frontward and backward. You will certainly have to adjust the teeth dimensions because I found that the good fitting depend on the printing settings..
You don't need belt clips (less parts). You may need to print a strap tensionner piece to adjust the tension of the head strap. I have to add some shims behind the tensionner for a better tension. See the strap.stl file.
I enlarged the parts that are in contact with your skin (like the Croccy22's design).
The elastic band idea of Croccy22 is perfect. I just changed the design of two of the four parts and add a little piece of tape (in red in the picture) for hold the two elastics in place all the time.
I added some very thin walls (0,3mm thick) as supports, for a better printing. You can easily remove them after.
KRAP_OPENDIVE.skp is my final design
ALL.skp is my sketchup constrution file (there is everything in it)
TENSIONNER.stl is the belt tensionner (just add some shims behind it)
Sorry for my bad english ;-)