It's a 2.0l carburettor fed M102 engine. Everything that fits a W124 or W201 M102 engine will fit on a 200T as well. Five speed gearboxes for example. However the 200T will need a custom prop shaft made (resp. the prop shortened) with a W201/124 5 speed. The W123's 5-speed (GETRAG 717.401) is much longer than the W201/124 5-speed (717.411 or .412).
The difference to the later W201/124 M102 engines is the manual valve adjusters, single row timing chain (replace it!!), mechanical fuel pump and oil filter housing, plus minor changes.
It's rated at 109HP. It's adequate for daily duties, but by no means fast. And it's the least economical gas engine (fuel consumption vs. power), expect the same MPG as a 230TE. All that aside, it's a wonderfully smooth runing, silent and reliable engine (mostly free of electrics or electronics)
And just like it's W201/W124 counterpart, the exhaust manifold likes to crack, welding is the best option as uncracked manifolds are as rare as hens teeth (or very expensive at MB's).
And as with any W123, the condition of the bodywork should be the main criteria for a possible buy!!!
Here is my '84 200T: