According to a Small Arms Review article, it appears that MK Arms did in fact make some open bolt semi-auto carbines for submission to the ATF technology branch on the cusp of the 1982 semi-auto open bolt ruling. Are there any still out there? Who knows, but the grand market of them were closed bolt semis.
THE SEMI AUTO MK 760 - Small Arms Review
By Brian ZuzeloPhotos By Christine Hillsmallarmsreview.com
Yes, indeed the most curious part of the article. I would love to see an example of one if there is one still out there. I don't recall coming across that in THE MAC MAN book, either."In the early 70’s, the MAC Corporation did produce an open bolt semiautomatic-only Swedish ‘K’ that was made in extremely limited numbers, and these weapons have faded into obscurity"