Thread:

454 valve covers

I just asked my engine builder, "the Bostick" about that. He said you have to have some sort of breather set up or you will risk blowing the seals out.

If you are buying a new set, I highly recommend the cast brodix ones, or a similar brand.
They come with 1/4" studs and nuts. The studs go all the way to the top of the covers and makes it so easy to remove and tighten.
Keeps the gasket in place perfectly and draws down nice and solid.

I just used a hole saw and hand drill to cut the breather holes where I wanted them.