Pics might be a little misleading but if you compare the two, you will see one has a new piece welded in to cover the open area at the baffle end. After I took these, I added a dent to allow the pcv valve more clearance, then drilled a 1/16” hole directly under the valve for oil drainage. Then I added the 1/2” spacers to move the valve covers 1/2” farther from the head and provide even more clearance.
Basically made sure there was clearance between the pcv and the baffle. Plus tried to keep any oil from getting above the baffle.

OK..........Nice!  You machine those spacers or mak'em outta wood or RTV gaskets or HOW??  Looks really slick.
6sally6

I have those same valve covers on my 351W. I had the same problem - oil being sucked into the pcv valve. I did the same mod as you have shown, but I used some thin stainless steel and bent them to fit. I cut down the bosses where the threaded rivets get driven into to hold the plates on. I originally had a problem with my roller tipped rockers hitting them so I cut down the mounting bosses. Once I installed them, oil problem solved. I regret that I didn't take any pictures of my modifications. I also have installed the covers with extra thick cork gaskets glued to the valve covers with a little grease on the gasket mounting surface. I have had the covers off a couple of times and they still don't leak.

There is a baffle on both sides, typically. But, since the driver side cover is just a a fill hole with fresh air INLET, there is no vacuum coming through a pcv valve to suck oil. It still must be modified or removed to clear certain rocker arm adjusting nuts.

A pcv system works by vacuum collecting blowby by sucking it out through the valve, while fresh air circulates into the engine from the opposite valve cover.  This helps reduce buildup of blowby gasses by sucking them out and burning them again. It also helps the oil stay cleaner.   I saw one car at the Waco car show that had a pcv valve but no fresh air inlet. Can’t state for sure if it was directly related, but that car’s oil also appeared pretty dirty.

That oil on the inlet filter is typically caused by blowby, or a worn out engine.  If everything is functioning properly, no backflow of oil should ever reach that inlet filter.

Be sure the pvc valve is not plugged up, too.

Stevo wrote:

That's amazing Steve. What made you try this? That was a significant amount of oil to lose previously.
Great to hear you fixed the issue.

 
After I changed cam and lifters, I removed the 1.25” spacers from under my valve covers. I had to percussion engineer the baffles to get them to clear my rocker arm lock nuts.  So, I knew there was potential for trouble.  Now I have 1/2” spacers molded to the valve cover flanges, along with modified baffles.  When I removed the pcv valve and the bottom of it was dripping with oil, it was a good indication that oil was getting to it.


Now the flanges on mine look just like these I did for Al McGee