I think most of the answers above are concerned with the differences between ETZ engines of different ages. If you're more concerned with telling the difference between a TS and and ETZ engine, that is much easier, although at first glance they might look similar.
The TS engine had a much more rounded crankcase:
Whereas the ETZ crankcase is a little more "brutal" with a noticeable step towards the rear:
The covers on both sides of the two engines are also very different from each other. Another difference not immediately noticeable is that the ETZ barrel and cylinder head both have more fins than the TS items.
To my knowledge, MZ never made a TS engine with an oil pump.
When it comes to the differences between ETZ engines, the main thing I think you are looking for is the presence of an oil pump? An oil pump engine will have a round cover with two screws fitted to the primary drive cover, behind the rev counter drive/clutch nut cover:
It's far more likely that any engine you come across will have external oil lines, but it doesn't really matter either way!