how can i get 400hp out of a 318?

Fresh set of forged 8.5:1 smog pistons, RV cam & 15psi manifold pressure.

Drive it to work every day if you like. No 7000 rpm grenade, no chinese stroker crankshafts, leaky headers, etc.

No, nobody makes a "kit" to turbo a 318. Nothing keeping you from doing it yourself. I built turbo kits decades ago. It was either "one kit fits everything" (and nothing well) or vehicle specific. We went broke doing vehicle specific.

Depending on which A body you are putting it in, fabricating a turbo install is not terribly difficult.

B.