Exhaust manifolds

Hi all. Happy Thanksgiving! Question; ive read that angle milling big block hi po exhaust manifolds will make them fit a Big blockA body swap? If so, does anyone know for sure how much to mill off and which bolts/ studs to mount them? After milling I figured the holes would be out of alignment. I’m using edelbrock rpm heads and a B engine. Which obviously has the lower deck height. Thanks in advance for any help! Mark