First I would mockup first & see how far the intake bolt holes (or better yet the top/bottom alignment of the ports) are in the "V" above or below dead centered in the intake manifold bolt hole "tunnel". this way when they mill the deck(s) they can mill the intake face more or less than the prescribed (.012 for .010) amount (as needed) so you end up with dead on alignment. they'll do the math to effect the slope change amt & you're paying likely the same or close to it anyway. EDIT wouldn't hurt to mill the head intake face and the intake. You want NO vac leaks.