You will ruin those heads doing that. For one, taking about half an inch of the intake face will cut in to the valve cover rail. Secondly, how is it going to change the intake port shape? If you ever decide to put those heads on an RB block, you're making spacers.
If I was so dead set on using the intake manifold, I'd cut the flanges off the intake and machine and weld on new flanges.

But, it's your money, do what you makes you happy.

I have attached a couple of pics, I don't have an account to host them. They are of a Trickflow 270 head (after I machined them for Jesel rockers) and on a low deck block.