I agree on nitrous or maybe a turbo but hate to see a hemi change it's looks
My suggestion since you don't want cam,headers, intake is to spend some money where it's best spent HEADS
Have the factory heads worked by a true machinist and have proper porting of intakes and the intake manifold, proper polishing of the exhaust ports and have the manifolds ported and jet hotted since you don't want headers, then tunes fuel system accordingly