How will i tell if the dealer really replaced my engine or not?

[ZYUL8R]

I pumped in apparantly 3/4 a tank of water into my Gas tank. This gas station had water in thier tanks. To make a long story short, it killed my engine.

Now the dealership has my car and in less than a week says they've replaced my engine...i find that hard to belive its not like VQ37's are just laying about.

Now maybe im wrong and they were able to get one this fast. But my real question is since they say its a new engine...Is there an engine stamp on the original engine with the VIN...when i pick up my car i want to be able to verify that an new engine was put in.

I just don't belive they could do this in 4 days time. I think they cleaned out the lines, and the tank, and just billed the insurance.

Any help would be greatly appreciated.