oh - you have the 601 4 cyl taxi mill. the M104 is from an E320, its the 6 cyl 3.2 litre engine.
It will fit onto the old cross member with original mounts, the automatic transmission will fit too, you can also use your manual box but would have to locate a flywheel for it.
The radiator, shroud and exhausts should be from an E320 and also require some special tools to fit properly.
let me check what differential your car has right now as Im pretty sure it would be a short one to compensate for the weak engine you have. You also would need a matching speedo for the diff (all e320s came with an electronic speedo and all diesels came with cable one)
The ECU will be placed by the OVP relay your car has, it must already have a hanger for it beside the ABS control unit, the wiring is easy for someone who knows what to look for - just would need to source some old MB wiring plugs to reuse (MB connectors have soldered pins and can be reused by soldering new wires)