Engine number identification

[drafious]

I'm in the process of attempting to purchase an Australian Delivered 2003 Z4 2.5, and trying to find out how i can get confirm what the engine number is against the registration. Reason I'm asking is because i understand that there can be multiple numbers. Could a mechanic get the id number and part number confused?

I've got this number from BMW
27055494

And this was from a non BMW dealership examination
75029001 or 750290001

Or does this mean that the car has in fact had an engine change? Can anyone comment?

I'm going to get the current owner to try and get a photo, but I would also like to know just in case I end up having to get under the car and check.

Thanks in advance!