Nick, I bought these cheap valve covers on Amazon and put a #12 bung fitting here and welded in a baffle like in Dave's photo of his.
I do not get any oil in the catch can, pull lots of vacuum and no leaks.
But, these valve covers are fabricated and oil will sit in the lip on the bottom rail. I had to put some Permatex #2 on the bottom of the valve cover gasket or it would weep a little oil.
Right now the driver side has a Erson stamped steel valve cover and it does not have that lip and never leaked.
Its on there temporarily until I can get my smaller brake booster installed. The fabricated one just hit mt stock booster.
https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1