I have about 18 1/2" hole drilled into the front of my box. I know a few others put 2 HUGE holes in the front. Not sure if one or the other is better, or if it even made a difference at all. I think I remember it giving me a little better throttle response.
Vinny,I have a link Randy sent me once(it shows a 300M-he did a bunch of mods including the TB mod-others are a cold-air intake and a functional hood-scoop) here it is300N
It's actually pretty sweet and the TB mod doesn't look too hard(although I'd have trouble finding the balls to go grinding away at mine)maybe someday...
Vinny.......I did it just like the 300M instructions and it went easy. I'm glad I hada buddy at a local garage take the TB off though. You couldn't pay me enough to contort for that long. It's way back there.