Rear end wrench

I tried a 1/2" socket extension on that plug in my 7.25" rear of either my 1964 or 1965 (forget, a few years ago), but couldn't budge that plug. I even tried heating it with a propane torch. I didn't try an impact wrench, but recall it was already starting to round off the squares, so probably wouldn't help. I just wanted to check the oil level. Maybe I need to try welding torch heat. If I drill it out, not sure where I'd get another plug.

BTW, the head bolts on my 1985 M-B diesel have a similar looking 8-point female socket head, termed "double-square". I had to buy a special socket which looks kind of like an allen wrench for them, but metric so doesn't fit the Mopar plug. Aerospace uses many 12-pt bolts (termed "double-hex" I recall), usually in male form, but a standard 12-pt socket fits.