Find an early 60's factory adapter plate from a Sweptline truck to mount a small block V8 automatic to a /6 and put an A500 or A518 OD automatic in it. Then you could run a 3.55 or 3.91 in the rear which would make it a lot snappier around town and still have a sensible cruise RPM on the freeway.

A 4 barrel intake and headers will make a very noticeable difference in the butt dyno if you stay naturally aspirated without doing anything else to the engine.

You are displacement limited so you are torque limited by default. A turbo is win win in that department as it will multiply what you already have.

Kevin