At the moment I am building up a GS300 and it has the same engine as a NA Supra.You can get 500WHP out of a NA with some big money and a good turbo kit ,some guys on the clublexus board have sc300 with exactly the same engine and 5spd tranny with over 500hp at the wheels.With a 2JZGE you canot fit many GTE parts on it so that cuts out all that side of the bolt on power ,but you can get a toyomoto turbo kit and upgrade that.If you wnat to convert your 5spd to a 6spd it will cost you a minimum of 2000$ for a good tranny and 1500$ for the install.I realy donot think a 6spd tranny is worth it if you are planning to upgrade your NA because with a good clutch and flywheel it will be just as good but wont have the extra top end speed.Go to Supra store and check out the FMax turbo kit it will give you 320WHP and can be upgarded as long as you do the right preventative upgrades to take the extra boost levels.Take my Advise and make you NA a real beast and remember to get a bad ass bodykit if you dont have one.
Here are a couple links so you can see the turbo kit.
http://www.f-max.com/fmaxlexusturbosystem.htm
http://www.powerhouseracing.com/catalog/supra_na/supra_na.html
