Scott,
Attached is a pic of an outstanding MK III single. All the MK III's I've owned or raced came with the NERF type bar on the rightside. Now possible the 1st few MKIII's could have used the little triangular type mount. They could have been leftovers from the Cheetah and Cheetah MK II
This MK III also has the "optional" LH nerf bar. It was bolted on instead of welded.
Jeff