The MK III, 22/45 is simply a variation of the MK III. It has the same LCI, magazine safety, key lock, and "American style" magazine release as the standard MK III. The only differences are the frame material, and the grip.
Same goes for a MK II, 22/45. Just a variation of the MK II.
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have everlasting life.
John 3:16 (NKJV)