Newbie 318 piston question

Lack of compression is the #1 hurdle to building a strong street 318. With the right combination of parts, you can make a real nice ripper.
IMO, a closed chamber is the place to start.
The swept on a .030-over 318(323.338 cubes) is a meager 662 cc, so getting pressure is often a challenge. Closed chambers will make it both easier and better.
For instance, to get to 9.7 with 662 requires a total chamber volume of 76cc. If you start with 72cc openchambers, you'll never get there with flat-tops, without head-milling at additional cost.
But at zero-deck with .039 gaskets you could be looking at ~62.4cc, Magnum heads are a natural. They've got everything your teener needs.