Question 1: If I have an old 220 line run to a condensing unit with no ground and I want to switch it with a 220 plug with ground for a wall unit, is it acceptable to ground to metal box if conduit is continuous all the way back to panel?

Question 2: Or, is it acceptable to use a ground from a switch or receptacle that is grounded all the way back to panel?

Thank you

If this is commercial work your electrician should be able to answer all this for you.