My theory, assuming its a well used and aged 318 and you probably have to replace or repair these items anyways is as follows:
1. exhaust. 340 hp manifolds or more affordable 360 magnum manifolds, 2.5" dual exhaust, good sounding muffler and depending on your budget H, X pipe . As a near stock 318 $150 each mufflers aren't necessary nor the cost of x or h pipe. Those would help down the road if you plan dramatically increasing hp. I like manifolds as it keeps the under hood temps down. Improving the flow and sound of the exhaust would ad power, some mileage and definitely smiles per mile.
2. Cam, lifters timing chain. Older LA 318, cams probably worn, plastic timing chain is falling apart. Nothing to crazy on the cam. RV cam sound about right. Maybe a cam with a slight rumble for the smiles per mile. On my motor i emailed comp cams with what i plan on running with stock compression. They recommended a cam. I'm happy with it.
3. Carb and intake. Switch to a 4 barrel set up, dual plane. Close to stock 318, 600 should be all you need. electric choke.
4. Heads. Since it will be a lower rpm motor, valve job. Make sure the valves are seating properly. 318willrun recent video is a good one. That's where i would spend the money.
Ive never been a chrome guy. A clean, freshly painted motor with stock valve covers, dual snorkel unsilenced factory air cleaner is what i like. My buddies have always lived by the moto, If it don't go, go chrome. We took the chrome money and went with cams, gears, shift kit and torque converters or put it towards the body.
5. Gears. If you have 2.45/2.76 gears, a bump to 3.23 or 3.55s would be a balance between mileage, cruising and off the line smiles. Not to mention sure grip. 2 black marks beat a 1 wheel peal any day. 8 3/4 would allow you to swap between gears depending on how far you drive. I run 3.91s but i rarely went on the highway.
Comes down to your budget, you can go hog wild in these areas. If you could swing ceramic coated heads they would look good and help keep the heat down. Adding fuel injection or roller cam would help but $$$$
Oh almost forgot, a 318WR sticker adds to smiles per mile and shaved .001 off my reaction time and et. lol