While they, the Indians and the Soviets did have some mutual interest in opposing China, the real rush to alighn themselves with the Soviet Union started when Henry Kissinger "tilted" towards Pakistan as part of the general sucking up to (he would say opening up of) Red China, which in turn was supposed to be as a counter balence to the Soviets. I thought it was dumb then, I still think it was dumb. Prior to that, the Indians bought alot of cast off, and new, British stuff. Their military, and Pakistan's too, is on the Brit model, more or less.
For the kiddies, that was during the Nixon administration, back in the dark ages of the late 1960s and early 1970s.