Sorry it took me this long to get back to you.
The helmet file you're working on isn't what I'd call 'game accurate' and wasn't modelled with easy construction in mind. I've often considered going back and modelling a fresh version from the game assets, and perhaps I shall at some point down the road. Plus, the Halo 3 Scout helmet has the misfortune of being poorly designed overall - in the same vein as the Halo 3 Rogue helmet, wearing the Scout helmet properly would mean the user's jaw would protrude significantly from the neck opening.
Food for thought, but don't let me discourage you from working on the helmet nonetheless!