This is one place where I know I can trust the answers. I have an ACH and wanted to do the same thing. The mount I have must be an older issue (Rhino? rectangular with one hole in front and two small ones on the clips on the edge of the helmet. If the newer triangular mounts are better, I'll get one of those to try out. What do you think?
http://twolftfeet.com/kit/ach_mount.jpg
Thanks!
Kathy