1. 1976 Cincinnati Reds
1B Tony Perez, 2B Joe Morgan, SS Davey Concepcion, 3B Pete Rose
Start with this: Joe Morgan posted an OPS+ of 186 that year, which is the highest for any middle infielder after 1935.
Morgan was a Gold Glove winner at his position that year and won his second consecutive MVP award after posting a career-high OPS of 1.020, with 62 extra-base hits, 114 walks, 111 RBIs and 60 stolen bases in 69 attempts. That was the fifth of six consecutive seasons in which Morgan scored more than 100 runs.
Oh, by the way, the first baseman, Perez, had 57 extra-base hits and eventually would be voted into the Hall of Fame. Concepcion, the shortstop, also won the Gold Glove and hit .281, developing into a borderline Hall of Famer; I don't think it would surprise anyone if some veterans' committee sometime voted him into the Hall of Fame.
And, oh by the way, the third baseman hit .323, with a .404 on-base percentage, scored 130 runs -- and later became the all-time leader in hits. Pretty good.
If you argued that the Reds' infield performed even better in 1975, that would be more than reasonable.