Doesnt look like a yz60 arm to me, the yz60 arm only has one of them vertical strengthening bars, also the yz60 arm mounts on the outside of the frame, that one looks like it mounts on the inside of the frame like the yz80h and yz80j, get him to give you the measurements
i can measure my standard yz60 arm and see if i is anything like it, that would look very trick on your 80j
60s where also only made from 1981-1983