You can tell would gear you have by givings us the engine rpms at 60mph in 3rd gear.
If you have a highway type gear (2.73 or 3.08), and you aren't willing to change gears then you need to make more low speed torque.
I would guess your car has a 3.08 gear plus those tires are tall which doesn't help gearing. If so, install some headers, compcam 260H, and a good set of 64cc heads (160 to 190cc ports). Power is all in the heads!
Later, consider adding more cubic inches (383 or 406).
You could also buy a used and "complete" vortec 350 engine from a 1996 to 2000 chevy truck. This engine makes a great starting point for a nice street engine (decent heads and a factory roller cam setup). Plus you could build the engine up while still driving the car. Check your local craig's list. But make sure to get a complete engine (fan to flexplate) as the little things will nickel and dime you to death.
I would not use an Air gap RPM intake on a street car because the intake is slow to warm up which makes the carb very unhappy in the cooler months. Plus it may not fit under the hood. Use a regular rpm intake and a holley 3310 750cfm, but check to see if it will fit first.