Air coming through the valve cover

Well a 268 is pretty big for a teener, and it's gonna want some bypass air alrightee.
Ok so first things first get a PCV and grommet plumbed in there and a decent breather on the other side. There's nothing wrong with the oiled filter you have on there now, except a few hours after installing it on a running engine, the oil will have all been sucked out of it, and the filter will now start to pass dirt. And whenever you go WOT, blowby will flow backwards through the filter and puke oil-mist all over your valve cover,and then the dirt will stick to that. So, if the breather on the passenger side passes air in both directions then use it and shelf that little one on the passenger side. Ideally the new breather should be plumbed to inside the filter house,between the filter and the air-horn. I know, I know , that's a PITA. So What you can do is install an exit hose on the breather nipple about a foot long and point it anywhere except down.Then the blowby will mostly leave it's oil in the filter or in the hose where it can drain back. But make sure both access points in the covers are baffled inside. The breather will require maintenance.
After this,the engine will require a retune.You can follow along here;
340 camshaft question, yea another one.

As to the oil; you can still find cheaper hi-zinc oils out there. They are labeled as diesel oils now, or Heavy Duty truck oil. But it was more the viscosity you chose that I was against. 20W50 is mighty thick. I tried 15W40 once and my pump blew the filter right off the pad and spewed oil onto the hot TTI headers. That coulda got ugly in a hurry. There are different schools of thought as to adding a Zinc package, I can't expound on that except to say that I have run it with any old cheap-azz oil since 2004 and for maybe 60,000Plus miles with no adverse effects. There are much better arguments for oil types, I'm sure.
Here is one;
More Than You Ever Wanted to Know About Motor Oil