Interesting to be sure. There's a member here who has made a subset collection of these rifles. Seems the 1963 is the last and hardest to find, IIRC. They used parts shipped over and had some barreled receivers in the mix as well, so never assume a mixmaster isn't right off the factory floor. I was lucky to find a Mk1 before they got "discovered". Interesting rifles, to be sure. Good find for you.