I say 420whp can be done with the spacers, tgvs, and inlet. Multiple reasons:
1. Hell its 11hp difference... you could change nothing but the wind could be blowing east instead of west the day you re-dyno and you get that number
2. As far as actual gains... you are putting the turbo/ic into a more efficient range that you can squeeze more boost and/or timing out of it. If you have more room on your fuel side you can def take advantage of the extra air aswell.


However since it seems as though you are doing it, hopefully you get better spool to make your car more "streetable" instead of getting beat by stock turbos below 100mph hehe