Harry,
I fitted a early 280SE engine in my 230SL as a temporary fix while I had the 230 engine rebuilt.
It must be a fuel injected 280 SE/SL engine out of a Pagoda or a W108 sedan (type 130 engine) which is very similar to the 250 SE/SL (type 129). In fact unless they are side by side, it would be very difficult to tell, unless you looked at the engine numbers or knew what you were looking for. I believe the last of these had electronic ignition which might make it tricky.
More experienced guys will know better and might elaborate on this.
Chris