reading through your inquiry it sounds to me like you are being offered a sedan engine (fairly common) in exchange for your 230SL motor (rare) the 250 and 280 sl motors were the same as the ones installed in sedans makeig them much more plentiful than the 2.3 litre motor that was only installed in the roadster.
the 2.5 and 2.8 litre motors had 7 main bearing crankshafts, the 2.3 had 4 mains making the flywheels not interchangable.
So the flywheel to fit up an auto would also need to be from a 7 main bearing engine.
Sedan engines have different motor mount arms,
It sounds to me like after doing all of this work, you would be coming out on the short end of this trade. Just my opinion, get the original 2.3 engine rebuilt. Fewer headaches, and the car and engine will be correct and matching
