The four of you above have not been very helpful. Quit acting like jerks.
To the OP's questions:
Yes, you need different brackets to rotate the monitor from horizontal to vertical. Post a WTB in the Classified ads section of these forums saying you need vertical mounting hardware for a classic Nintendo cabinet. Expect to pay about $50 for everything you need.
While I don't doubt that it might be possible to create some kind of rotating wood frame to allow the monitor to spin from horizontal to vertical, I would seriously discourage you from trying this. Nintendo cabinets are not wide enough to allow for a monitor to spin inside the cabinet without hitting the sides. You would either need to widen the cab (no!) or cut holes in the sides to allow this (no!). If you're hell bent on having a rotating monitor setup, just put a 19" 4:3 aspect LCD screen in there and run the cab using an inverter and CGA/VGA converter. Then you can rotate the monitor easily.
The blue finish on the DK cabs is not vinyl. It's a gel-coat finish applied at the factory, and it's not removable. You can sand it down to bare wood, but it's a LOT of work and not really worth the effort. If you want to convert the cabinet to DKJr orange, then just sand/repair the sides, prime, then paint in a matching color. Another option would be to prep the sides, and purchase orange vinyl from This Old Game.
Hope this info helps.