Honestly fellas, I don't see why anyone would view the insertion of the visor being anymore difficult on this helmet than the standard Mk VI. From what I can tell of the plans smilie posted in the first post, the CQB helmet has roughly the same forward curvature for the visor. Therefore, one can still use a replacement visor for this build. You can do it one of two ways:
1. Trace the outline of the visor area on the replacement visor and cut it to shape (with a Dremel or some other motorized cutting tool) to fit snug in the opening;
2. Leave the replacement visor intact and simply adhere the unseen portions to the inside of the helmet. It'll still look like it's supposed to, but less work is involved on your part;
And there you have it. Seems like a pretty simple task to me. Then again, those are just my suggestions/opinions on how to handle the visor aspect of the build. Take it or leave it...
P.S., Your CQB helmet's looking good so far, buddy. Keep it up...