The magnums are machined. Us poor LA guys have to file +Dremel away. I should have taken pics , the casting porosity makes me wonder how any LA valve covers sealed.
I ALWAYS use the black Felpro rubber gaskets and RTV on both sides on LA heads and never a problem until I put fabricated aluminum covers on my old motor ( stock cast heads 318)
There was an 1/8 gap both front and rear without the gasket in place, so I cut about 6 inches of the ends off another set of the rubber gaskets and laminated the two end sections together with the first set, then used a moto tool to taper the two ends I added down to the original single thickness in the center of the gaskets.
That did it, but it was a lot to go through for it.
I have the Magnum with EQ heads in the LA intake bolt pattern now, and boy that was a breeze.
Both surfaces machine flat and the OE steel/rubber reusable valve cover gaskets are fantastic.
