Cheap 318 performance mods.

If leaving the 302 heads stock, I wouldn't bother, time and money for no real gain.
You a least want to gain head flow if doing a swap, A magnum head or milled 360 swap keep/gain cr while giving more flow, if willing do some porting can add 273/318 heads back in the mix but you can also port the magnums or 360 heads.

But really you can skip all that if it's a decent runner just the basic tune, cam, 4bbl and headers can do a lot especially with gears and a stall.

Here's a stock low cr 318 with 4bbl, headers and comp cams xe262h for 282hp @ 5000 rpms.
https://www.motortrend.com/articles/mopp-0312-318-long-block-bolt-ons/