Off the top of my head there are many differences such as
Cylinder heads
Engine mount bolts either 8 or 10mm
Ancillary brackets will not fit certain models
engine wiring harness plugs differ
Starter motor can be mounted either left or right
Its the last 3 digits of the engine code you need to match up to ensure it will fit.

These om642 engines knock out number one main bearing if you neglect engine oil changes so the one you are going to look at in reality is not a feasible option unless you intend to completely strip it out and rebuild