Make sure you're intake gasket centered right check the valve cover bolts in reference to the center common wall to light them up...and the right height, how they sit on the china walls/cork..or else glue them. When you grind them out lean the grinder so that you're grinding it to that line then you'll open it from there and if you leave just a little bit and I mean like a paper sheet thickness you can take some nice flat files and dress all of those perfectly straight and a nice little round file to get the corner in it's just for Aesthetics it doesn't make more horsepower or anything that you can measure. A good backup if you go outside the lines to get yourself a metal straight edge/ruler & razor blade take a skin off of the outer diameter of that Port window on the gasket inside that sealing bead and then you can grind to that get it right again and do it on all of them from there so they're all the same if ya want.
