I'm not sure when they changed from an external to an internal regulator. My 1973 280SEL (W108 - actually a '72) has the external regulator bolted to the back side of the ECU. Take a look at the backside of the alternator, you should be able to tell if the regulator is internal.
If the alternator looks like this:
you should have an external regulator. Sorry I don't have a picture available of an internal regulator set-up.
Hope this helps.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.