I've seen A LOT of posts about making HP with a 318-So why is it so ???

Mmmmmm, 450 tq? Noooo.
350...... maybe.

Where it ended up would most likely come down to just how good the heads were, and what you did with a cam.

My “upgrade” from that combo would be a small solid cam.
Stock 318's have around 340 stock.