Intermittent crankcase pressure issues

Deceus said
I had intended to try just running double breathers for a bit but never got around to trying it. My dad built a nearly identical 318 8 years ago and never had any of these issues which is what I'm basing most of my reasoning on. Chances are if he got away with the setup he's running (the same as mine) then the issue is definitely elsewhere. There may be a more effective way to manage to blow-by for sure but right now my main concern is definitely tracking down the source. A fresh mild 318 shouldn't be having these problems.

No offense but from my experience that kind of thinking leads to nowhere ("it worked with his setup so it should work with mine"). Your dad probably got lucky that both the breathers he happened to use could flow enough that the crankcase didn't over-pressurize. When the PCV valve senses pressure it shuts and forces the crankcase gases out the breather side; with 2 breathers the engine has 2 big holes to vent out through at all times.