Here's a little idea that we tried on my friends motor. With the intake off, stuff some rags down each intake runner on the heads. Run double sided tape across the intake face of each head. If your tape is not wide enough, make sure it just butts edge to edge and no overlap. Then stick some strips of sand paper on the tape, grit side up. Start with course grit and work to finer. Place the intake on this and slowly slide it back and forth to match the surfaces. Depending on how far out the intake faces are, this should not take very long. Once done, you should have perfectly matched faces of intake to heads. Caution, do not go overboard on this as to cause misalignment with the ports.