header to motor mount clearance

I have a 5.9 magnum I'm building a 408 stroker out of and my question is about header clearance to the truck motor mounts. I have hooker 5116 headers and I have read on the magnum swap page that the truck mounts have to be ground down to clear the headers. Anyone have this issue before? If so how much did you remove and pics would be great. The block is at the machinist and it's a bit of a ride to go down there to mock it all up and realize I have wasted my time.
Thanks FABO