318 question

That's the thing, looking for the easiest combination to get to 300
I'd get rid of the "300hp" goal,

1st I would decide what gear and stall l'm willing/gonna be running
2nd headers or manifolds
3rd heads stock or mods to the heads or different heads.

Better heads need less cam to get there, bet a stock 5.2 magnum has 90% of your power goal unlike an LA's 60%.

Then decide what cam & cr will work and it makes what it makes.