Little 318

You certainly may perform head work at any time. On a stock bottom ended 318 I would limit my choices to 4 choices in whatever order.

1)302 casting heads needs port work to make serious h.p but 350-75 h.p without is doable.Plus they offer the best compression bump due to thier small chamber.

2)magnum;While not a true direct bolt on it is close and requires maybe an extra $125 over an la style heads for the adaptation parts. Also has a good size port for a teen and wont require head work to make 400 h.p.There is also a comp bump. There are very good aftermarket mags now,much improved over stock. I suppose the ultimate mag isnt really a mag. The rhs heads have la style rocker shafts,mag combustion chambers etc.The eq mag is just a greatly improved stock config mag.

3) 340/360 La head. A bolt on mod but gives you ports that are a tad too big for the cid of a teen. Result is not much bottom end torque compared to other heads but a huge top end and mid range. Makes for a great rpm screamer but need to have the heads milled to get comp up. Huge chambers drop the comp into the 7.5:1 range with stock pistons so not a great choice with stock pistons.

4)stock 318 head. Im a personal fan of this route as well as the mag heads. Reason being is you already have em. All they really require is some 360 1 .88 valves on the intake,some port and bowl work and they are probably as good as a 302 head,minus the fancy heart shaped chamber. But they still have a smaller chamber than the 340/360 heads. Obviously comp ratio wont change one wit without milling.

Theres no clear advantage from head to head. It all depends on what you can afford,what you already have,etc...