You need to set the new intake on without gaskets. Look and see if the bolt holes line up.
If they do, measure whatever intake gasket you are going to use (not the steel shims gaskets I hope...they are hard to seal in a bimetal application) and that is how much you mill off each side of the manifold.
You also need to mill some off the end rails of the manifold.
DO NOT slot the holes. You’ll get the bolts in, but the ports won’t line up.
