Engine number ground off, any other way of IDing it?

[Narcoleptic]

I have a '82 240D automatic that I'm trying to find out the engine number to order parts. The PO told me that the engine was swapped for a lower mile (no idea what happened to original engine) unit. I found the location where the engine number should be, but it looks like everything after 616 was ground off. There are marks consistent with a wire wheel on the number area.

According to this post there is also a plate fastened to the block with the number, but doesn't specify the location. Where is the plate usually located?

I'm the part I'm stuck on is a thermostat. Going through both engine number selections, it seems the part number is the same. Is there a different in thermostats, or is it just a opening temperature difference?