This is one of those questions were there is probably no "Correct" answer. a lot of these were fitted at the dealers, probably by the young "Gofer" who put them on what ever side he grabbed first. Also as would be the case in the factory at the time of build. Don't get caught up on the smaller details, We have seen many genuine new bikes straight out of crates that aren't "Correct" to the parts book.... Remember these were built in factories punching them out, Not spending 3 days to fit fenders checking everything to the .001" We have a brand new NOS Goldstar scrambler here, never sold from new, we are the first owners, never started.. The frame decal is upside down, Engine pipe is hard against the frame, and has different bolts from one side to another on the fenders... They were never built "perfect"
"Most" would be tach on the left, but its also a case of what you, or the buyer at the time prefers.