I am looking at buying a used Whirlpool microwave that was mounted against a wall to replace my Hotpoint microwave that is mounted over an island (under cabinets & cabinets on the side with a board covering the back). They are both 30" wide. I'm wondering if the mounting parts are universal so I could use the same parts. The guy selling his says he only has the wall mount. Is this a difficult job? Thanks for the help!