103 is the engine type, 3 litre straight six, cam in head, 12 valves. Was fitted to 107 (SL sports car) 124 (medium size saloon, estate & coupe) and 126 (S-class saloon) from 1985 to 1991 ish.
983 is the sub type, and this was only fitted to 300Es, although some of these had sub type 980 fitted, can't find out what the difference was. Your engine did not come from a 4-matic, sub type for those is 985.
I guess the only way to find out the year is compare the rest of the numbers with others.
You could try a post on alt.auto.mercedes newsgroup, there is someone who reads that who has knowledge of production numbers.
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)