Swapping the engine would be more work than it's worth. The wiring harness is going to be different, ECU, ignition control, radiator and other bits. You'll also probably want to swap the transmission for the correct one to match the M103 and put in the proper rear diff so the car would be able to move under its own weight. Parts alone you'd be better buying a 300SE or fixing the M117, let's face it, these cars aren't worth a ton anyway.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.