318 LA build

The problem with stock 318s, from a performance standpoint which gets worse the more performance you want to extract, is the lack of compression. These motors were built for mileage and long life not horse power. Standard 318 heads use small runners, valves, big-ish chambers and were combined with low compression pistons. Here are some options to consider:
302 heads have a great heart shaped and smaller combustion chamber (ups compression) but still utilize small runners and valves. To really make them flow you need bigger valves and lots of port work. Used are prone to cracking.
Any 360 head will have larger runners and valves (1.88 int & 1.60 exh). The combustion chamber is even bigger (lowers your compression even more). Going for 2.02 sized valves won't help as the low compression can't utilize the additional flow. You can mill the head and/or use thin head gaskets to up the compression a little. But too much milling requires the intake surface (on head or intake) to be cut to keep the intake seal and the ends where it seals to the block may need shaving also.
The answer to solve the problem is pistons to match the performance level (compression) you want to achieve and then match the carb, intake, cam, heads and headers to that level. The 318 can be built from a put-put to high rpm screamer. It's all determined by your wants and wallet.
Two nice running, cheaper, base street motor options:
Stock pistons: Keep 318 heads, matched intake (318 sized runners), 600ish carb (if Holley use Vac Sec), 340 type cam, headers of choice. If you can find uncracked 302 heads for cheap would help raise the compression.
Zero deck pistons: Here the world opens up. To stay low cost use stock 360 heads with 1.88 and 1.60 valves. Bargins on these are everywhere, I just picked up a set completely rebuilt, new stainless valves, new 340 springs for $300. Keeping the smaller valves keeps flow velocities up. 360 sized intake, 268 type cam, 600 - 670 cfm carb, and headers of choice. You can vary from there per your budget. Many will have all kinds of recommendations but these basic motors are good places to start.