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

QuickDart360 said
By any chance do you remember the cam used? Hydraulic or solid?

It’s right in the original post:

Reworked 675 heads, 340 cam, Performer

It was a “Perfect Circle” brand, stock replacement cam for a 340, that came out of a used re-ringed low CR 340 I had laying around.
The exact same thing as a Sealed Power CS644.