I do not know this specific model but IIRC there were plenty of fixed weapon armored vehicles in WWII.
Some things to consider:
You can lay one hell of a slab of front armor without worrying about turret rotation
Simpler to manufacture and maintain without turret rotation machinery.
Larger and or longer barreled weapons can be used since you are not worried about fitting it into a turret.
I concede a couple of your points. First there is the Abrams, and then everything else. Second I agree, the M-60 was not the pinnacle of design, or any great break through in technology. Still, at the time it was the baddest boy on the block at the time, while during it’s own time the M-4 Sherman was outclassed by everything else out there. Yet the Sherman makes the top ten and the M-60 is ignored. A little dispute in the mideast during the 70’s confirmed the M-60 totally out classed the Soviet made alternatives.
The only reason the Sherman made a difference was the huge numbers, and the exceptional bravery and skill of thier crews. The crews deserve all the praise than can be given them, but the machinery was second rate at best.
And as a disclaimer, I was not a tread head, I was infantry. You could not have gotten me to get into one of those cans. To paraphrase Bill Mauldin, “A fifty two ton moving foxhole attracts a lot of artillery”. To further disclaim I was in from 80-86, and blessed with the only time in memory that we were not shooting at anybody, the closest I came to combat was a bar fight at Ft. Benning. And I never saw an M-1. I do not dispute your facts as far as one having been built in 78, but that hardly makes it a viable resource at the time. If all heck broke loose at the time, it would not be M-1’s holding the line, it would have been M-60s, and they were up to the task.
I haven’t had much (read anything) to do with the armed forces, or with armored forces in particular, since the mid 1980 when I left the Reserves. However, in one of those European Reforger war games in the mid-80s the Abrams had just been issued out to the US armored divisions in Europe and the fall games were the tankers first chance to use them in large scale maneuvers. The tankers were just ecstatic. They had nothing but praise for the new tank and were just about giddy when they started talking about encounters with M-60 and German Leopard equipped formations and British units. The guys who were using the Abrams were pretty enthusiastic about them. Encounters in Gulf I, albeit against an inferior adversary, seem to confirm their opinion.