1966 Dart D-Dart cam spec

Not to steal a good thread here but I have a question about grinding cams.

If you send in a core with smaller lift heights and smaller base circles- how does a machine shop “regrind” a cam larger?
For $79 they are not welding to your cam AND regrinding it. Anyone care to explain?

Because they can put that lobe "anywhere" on that camshaft core they want it regarding the camshaft centerline.