You can...my buddy had all the NA mods on his car...and was also running low 15's at best...it is very possible to keep all that (well of course the headers will need to go) and still go w/a custom turbo kit...he made his for around 1600 bux and puts down around 223rwhp at 5.8 psi...
Here's his site...check the dyno graph at the bottom of that said topic...his setup is as such
Custom Turbo setup: T3/TO4E, RevHard manifold, 370cc injectors, Hacked MAF, 2.5" downpipe and full exhaust, TiAL 35mm external wastegate
w/that and his TEIN's and his whiteline's...and Azeni's on some new 17's he just got...he kicks much tail at the autocrosses...
His site is:
http://www.cautioncreativity.com/briand/
or email him at
[email protected]