Adaptation First: The NES version was the first version released in North America, as the MSX2 standard was never available in America. Although technically a port, it has enough differences to be considered a separate game.
The Fear's voice wasn't the first time his voice actor (Michael Bell) voiced someone from a military unit called Cobra. Neither were Volgin or The Pain.
In the original, the DARPA Chief (Greg Eagles) was Gray Fox (and Stillman), and both were also the Grim Reaper, Luke Cage and Aku Aku. In The Twin Snakes, the Chief retained his voice actor, but Gray Fox was recast. He was then voiced by the same guy who did Bubsy and Pinky.
Rob Paulsen also voiced Raphael, and Gray Fox is killed by Leonardo. Eerie coincidence!
Dragon Ball: Kenji Utsumi (Volgin) voices Recoom and Sheng Long, Daisuke Gouri (Lt. Cunningham and Scott Dolph) voiced Mr. Satan, Chikao Ohtsuka (Big Boss) voiced Tao Pai Pai, Shozo Iizuka (Peter Stillman) voiced Nappa, Norio Wakamoto (Gene) voiced Cell, Hiromi Tsuru (Naomi Hunter) voiced Bulma, Kozo Shioya (Fatman) voiced Majin Boo, Yukitoshi Hori (Vulcan Raven) voiced Cyborg No. 19, Toshio Furukawa (young Roy Campbell) voiced Piccolo and the late Takeshi Aono (old Roy Campbell) voiced his father, Piccolo Daimaoh. And while she didn't voice any character in any Metal Gear game, Miki Itō (Cyborg No. 18) was the voice director in the Japanese version of the first Metal Gear Solid.
No Export for You: The MSX2 version was only released in Japan and certain European countries. It wasn't until its inclusion in the Subsistence edition of MGS3 that it got a wide release (particularly in America).