I have had three of them. Two were the M70 Super Grades of about 1971 vintage. 22" barrels.
I picked up a supergrade.458 in the 80s, and it looked to have some age on it, so I gather it was something from the 70s Wasn't too impressed with the stock inletting, how were yours in that regard?
-Bulletproof and Waterproof don't mean Idiotproof.