peripheral port is the only way an NA is going to see over 300 hp
and you'll get pulled over everytime you drive on the street because
they are ear bleedingly loud
swapping in the TII drivetrain would be a much more cost effective plan
buying an actual TII would be even cheaper in the long run

what are you doing that you feel you need 350 hp?
and why had you not done research on these cars before hand?

Point being that my unmodded bone stock S5 motor has gotten the car past 140mph
and I can hang with anyone through the corners at speed.
So really you ought to just learn what the car can do before increasing the power.

edit:

after looking at the car I'd say you should either learn to enjoy it for what it is, or sell it to someone who'll appreciate a low mileage good condition S4
fix the headlights and post it on the RX7Club.com - Powered by vBulletin for sale forums
you should get $2500 to $3000 for it.
While you're there thoroughly read the information on these cars in the second gen forum, I learned a ton from the site.