The serial number on the engine wouldn't match the VIN (even if the engine hasn't been changed). Go to MBUSA's website and follow the links to their Classic Parts Center (ClassicParts@mbusa.com), and e-mail them. Give them the VIN (not the engine number), and ask them to send you a data card. They'll e-mail and hard copy you the data card, and it will list quite a bit of build information, including the "motor" number. If it doesn't match, it's a replacement. They don't even charge for the info. I haven't read your other threads on this topic, but if the car you're talking about is a '75 450SE the engine serial should start with 117.983. Other numbers would indicate a swap. For instance, after 75 the 450SE engine was 117.986. My 75 450SL should have a 117.982, but has a swapped 117.981 from a 72/73 300SEL. Apparently a 4.5 is a 4.5, so I wouldn't be too concerned if it's not the original. Good luck.