The 560 only came out in 1986 but I have seen several earlier models where the owner for some reason changed the badge.
Just a glance at the engine from a fairly good MBZ mechanic and he can tell which engine it is. If my memory serves me correct the 380 is a noticably more narrow engine than the 560. My 82 380SL has a 560 engine and trans and at a LA GTG this past summer we were comparing to another 380 parked by me. The man who knew all the differences was Mike Tangas. You might email him.