Need help on first time rebuild 318!!

You can build a 400 HP stock stroke 318, but it will be expensive. You cannot do it easily without ported heads and they don't come cheap.

However, if you find a good 360 core, it would be much easier to achieve 400 HP and it would do it at a lower RPM than the 318 and that would make it more street friendly.

HAVING the 318 already though may be better. It all depends on your budget.