thats what I'd do is use the thin .015 gaskets on either side of the valley pan. I would mockup dry first to see how the bolt hole alignment plays out with the addition of the extra material & it may need to be milled just for that which would kill two birds with one stone on the warped potential. If I went to the expense of milling I would first put a swath of dykem horizontally across the top and bottom of the intake and head ports plus go around the corners on the ends so you can see the scribed lines when the intake is sitting in place, then scribe a line in it (top/bottom/corners) with a pointer with a 90 deg "turnup" on the corners (if that makes sense) so you can mockup & see how far the ports are misaligned (get the intake even side to side) then give that dimention to your shop so they can mill it the exact amt so the intake will set further down into the V to get the ports dead on. if the intake is down too far as is then thicker gaskets would be needed to go the other way. For cheap I would mockup & see where the bolt hole alignment falls as is & if it is acceptable (with or without paper gaskets/milling ain't cheap) then use a copious amount of some good gasket cement on the valley pan (Permatex #1 or #2 in the toothpaste like tube or "the right stuff")