[Ptero]

If I had that car, I'd slap some Extreme Low Rolling Resistance (ELRR) Pirelli P6 Four Season 185/65R14 23.3-inch diameter tires on the front. Get some 15-inch rims on the back, if they'll fit, and mount 185/60R15 P6 24.5-inch diameter tires on them. That will give you a mild overdrive (~1.05) - about 5%over running OEM 14s on the rear. Put a spacer in the rear springs if you need more clearance. I think they'll fit with no problem.

Next, put a straight-through muffler on it (like a glass pack). Headers and/or a wider exhaust pipe would make a difference.

Make sure the A/C clutch is working and disengaging properly.

Make sure the radiator fan clutch is working properly and the fan shroud is in good shape with no more than 1-inch clearance to the fan tips. Test the radiator cap or buy a correct new one. Install a winter thermostat but only change it out to a summer thermostat if the car develops a tendancy to overheat.

Change the oil over to Synthetic Blend (not full synthetic). Replace the differential fluid with pure synthetic. Lube all fittings with mollybnium, expecially the driveshaft.

Install a high performance coil, new plugs, new plug wires, properly routed with proper standoffs so the wires do not touch metal.

Pull the carb, rebuild it and re-jet it to the smallest jets. Reset the valves just slightly and evenly loose, not tight.

Eliminate all vacuum leaks. Spray starter fluid at the base of the carb, intake man, vacuum hoses, etc. If the rpms increase, find the leak. Be careful of fire.

Make sure the air cleaner filter is the proper size or better yet, larger. Make sure cold air is routed from the grill, not hot air from the engine compartment.

Make sure the gas cap is sealing properly to prevent evaporation. There may also be a charcoal cannister. It can be bypassed but the hoses should be reconnected to each other.

Advance the timing slightly but do not allow pinging under load. This engine may have been retarded in OEM specs to minimize CO emissions but now may no longer be subject to those regulations in your area because of age. I suspect 4 to 6 degrees but I'd listen under load to be sure. Always drive with a light foot. You'll get 25 mpg without too much effort.