I am not familiar with an M1A3, we don't even have them yet, the M1A2SEP is the latest.
I served in the Army in Germany in the 80s. The US tanks in service during those years were the M60A3TTS (until 1989), M1, M1IP, M1A1 and M1A1 Heavy. There may have been M60A1 RISE/Passive in the early 80s as well.
Ask him what his MOS was. If he was a 45E, he would have been an M1 turret mechanic and worked on the Abrams series. If he was a 45N (I think they were Novembers), he would have worked on the M60 series tanks.