Summary

used the easy mask of shiopyon, but i use head straps for this, (single head strap, loops through bottom, goes through top, ties in back of head - i also made 3d connectors for that but you can just tie it.
also, (I used sketchup), i CURVED the inner parts of the strap guide, because when pulling them against right-angle edges, the strap would bind up.

i also cut the side piece of the bracket, and i just sew a channel in the material, and the material can slip onto the upper and lower arms of that bracket.
i can detail this more if needed.

the material is N95, 3 layer, www.filti.com, and it is easy to replace teh material onto the side clips.