300 HP out of a 318, is it possible with bolt ons?

I would think that is a definite possibility. Heads and their associated airflow could be your biggest problem.
I do have one question though. I have always considered a "Bolt On" to be something like headers, intake manifolds, etc. that we bolted to the outside of a motor. Would we consider a cam swap to be a "Bolt On"? PLEASE don't get me wrong. I'm not trying to hijack the thread be negative, I am just seriously curious.