Why are 318's low HP and torque?
What are you using the car for? Street/strip? Weekend cruiser? I don't know where you guys are living but here in Oklahoma, 450 hp is more than enough for the streets.
This is a great read and a great explanation where the 318 was lacking. Basically compression boost (decking) vs. Head flow and valve size is where you will get your greatest increase.
http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/viewall.html