I used the the of http://www.thingiverse.com/thing:734608 to create a goggle attachment for my Ops Core helmet, Arch Rail mount. They slide in on the lower back part of the rail to create a bracket to attach a set of goggles to. They are not pretty but they are functional. The set published here is the final set, the set i printed and tested had a few flaws (too long, and some overhangs).
For this set i suggest printing 15% infill (or more). The L and the R fit inside, so as to not be visible, but to aid the user to slide them into the correct slot. edges my need rounding with sanding paper - they may be a bit sharp post print, shaving though goggle elastics. The angle of the straps is set at roughly horizontal - so just move the attachments up or down until eye height is met. Also, they are at a slight angle away from the helmet, this is to accommodate for headsets - thus allowing the elastic of the goggle to go on the outside of any headsets (i dont use a flip up headset attached to my helmet, but rather one that fits over my head, under the helmet). Any questions please feel free to ask