I know I'm reviving an old thread but I just installed it and at first I was not happy with the overall fit. Yes I followed the directions. I ended up tacking on a few little brackets on the bottom side of the inner mounting face. I had popped the hood twice after installing it and noticed the top of the filter box had slid inwards.
I ended up taking that inner piece off with the 2 prongs and tacked on a quarter of an inch onto the regular tab a right angle, slid it up while the rest of the housing was installed then screwed it down. Since then no movement. It sounds great, btw.
Another small little thing I'm fabbing up is a little brack to mount on the nut just the to the oustide of the box to display the supplied stickers. Yeah I'm a nerd.