I have the same thing in my 67 gtx...I put in the edebrock heads,509 purple camshaft,holley 850 carb ,hooker super comp ceramic headers with full on msd ignition...I gained about 60 hp....So i now have about 435 to the rear wheels...It,s really pretty easy to add some h.p. when you start out with 375 in the first place...Ma Mopar really underestimated the true h.p of their engines...They say this was for insurance reasons.....MOPARS RULE!!!!