Well, I would say this about that. First of all, if the prime directive is just a NV mount, get a bump; it's what I wear 95% of the time.
If you need ballistic pro (for a class or something) there are many more cost-effective options.
If you just want to have fun doing some kind of mod, go for it. I have done several helmets myself, when ACH's were under a hundred bucks and cutting them down made sense. But at the end of the day, they're still pretty heavy old tech. But you can now mount rails n muffs an lotsa other stuff.
Best way I have found, rough cut with a thin mitre saw, then grind down closer with belt sander. Final finish with sanding drum on a Dremel. Re-seal edges with a good 2-part epoxy. Re-coat with your favorite finish.
These were great mods back in the day. But they've been over-taken by new tech. The juice might not be worth the squeeze any more.