R107 380sl Engine Options

[mjcobb]

Having just a bought a nice 1981 380SL with the original single cam chain and 130k on the clock I'm torn between doing the chain etc. replacement or just substituting the engine completely as there seems to be a plethora of 420 & 500 cars available as donors for little money. Can anyone tell me what the complications might be using either the M116 420 engine & gearbox or the M117 500 in the SL (if I use a W126 saloon as donor)? I'd appreciate any help - Martin