Also, first flight of the Hind was in September 1969 - the Sikorsky concept attack copter concept was only a proposal at the time and didn’t fly until the following year.
The Sikorsky S-67 was a further development of the S-66 program begun in 1964
http://www.sikorskyarchives.com/S-66%20AAFSS.php
The Mil-4 (1952) was a copy of the Sikorsky H-19 (1949)
https://en.wikipedia.org/wiki/Mil_Mi-4
“The Mi-4 was designed in response to the American H-19 Chickasaw and the deployment of U.S. helicopters during the Korean War. While the Mi-4 superficially resembles the H-19 Chickasaw, it is a larger helicopter and is able to lift more weight.”
The H-19, H-34 and Mil-4 all had radial piston engines located in the nose below the pilots and driving the rotors via a diagonal driveshaft.
The SH-3/S-61 & the Mil-8 have turboshaft engines above the cockpit with a driveshaft heading straight back to the main transmission & rotorhead.
The SH-3/S-91 first flew in March 1959.
The MIL-8 first flew in July 1961.