Just my 2 cents since this was my first mod and I could be doing things wrong:
I have done the same installation on mine FX35 last Christmas and noticed the followings:
1. Stillen included 4 longer bolts but didn't mentioned what those were for in the installation manual. I was stupid and naive (so I wasn't take tic tac) since that was the first mod and didn't realize those 4 bolts were to replace the OEM bolts since they are not long enough. After trying really hard on using the 4 OEM bolts (tried an hour scratching my head...and sweating all over in my <30F garage) , I gave up and went to Homedepot to get some longer bolts....then I realized those bolts were actually offered by Stillen. So if you received those bolts, use them. The OEM bolts might be barely enough if it is hotter (just joking....they are too short in my opinion) and it was <30F that day. Go get longer bolts from any hardware stores.
2. My rivets were broken and just hang there without any real function. But so far after maybe 5k miles and I haven't had any problem.
3, There is another bolt that fastens the Power Duct to the side of the engine bay. It wasn't an easy fit for me. I can barely get it fastened while keep the rivets in place (that's why the rivets are just hanging there now without function).So far this bolt seems to keep everything in place.
4. It took me some twist to get the Z-tube in and the vacuum hoses attached. It was a tight fit and the whole setup wasn't totally straight (pretty much like the pic shown in the previous post).
5. I did notice a more aggressive sound but can't tell much power gain through my Butt dyno. I did feel (maybe just physiological) a stronger pull in mid to high rpm after installed the Mrev2 + 5/16 spacer.
Hope this help