If you don't have overdrive, you won't enjoy 3.73 on the highway. I run 3.23s which aren't terrible at 60-75 MPH, not rodding the guts out of the engine.
3.55s are the best of both worlds, you give up a little on top end with higher engine speeds, but more low end grunt. Mine jumps at low speeds with a throttle tap and its a 318 with. 3.23s. (Healthy 318) Headers and intake will be your most noticeable power gain. You'll enjoy the car so much that eventually you'll pull the engine for a complete redo. Then you get to make all the really fun go fast changes! :)