building a mild Daily driver 318

I added a (Ancient Edelbrock) LD4B, 600 AFB, Hooker headers into a Jegs 2-1/2 exhaust kit and a Crane Cam 216/228-,454/,480/112. A dead stock 904 trans and 3.21 posh with stock tires. All this on a very low compression 318 (mic'd lower than 8.0-1) and its stock heads.

First run OOTB & on the verge of over heating was a 15.14 @ 89. 18 mpg Hwy.

Considering a 180lbs. driver and a half tank of gas on a listed 3K plus car, it wasn't to bad for bolt on's and a cam. A little more compression would have helped a little. Porting the heads with a larger set of valves would have been great. Also considering the valves are 1.78/1.50 in size, it could afford to breath better through some larger diameter valves.

The next cam size up, would prove to be a nice help in your goals.
If you can do your own heads, an inexpensive route would be used 360 valves (1.88/1.60) and some bowl work/gasket matching. Shaving down the pushrod pinch in then take ports.
That would save a ton of money. Though not as much (potential) HP.