not worth it.
you can get like a C43 motor, the transmission, then you will need to get the diff from it which may even have to have the C43 driveline and rear axles (not sure of that)
then you need the engine harness, and the ECU. the ECU may not even plug and play you will need the body harness - which is the wire harness for the entire car. the ECU will have a differnt VIN and which wont match the EIS and wont let your car start. you can get the VIN matched to your EIS BUT if you noticed- your car will have either a DAS I,II,III system, DAS III is the cars with the newer smart keys I think all C43's came with smart keys.
so its way too much, trust me ive done research on this and it wont be worth it.
if you have a C180, I think you can choose between the C200. C220, and maybe even the older C230 motors without the SIEMENS fuel injecters.
if you have a C280 I6 you can swap a C36 motor.
C43 can swap the E55 motor,
I think those are the only options you can go to.