Mercedes Benz 350 SLC and 500 SEC

Hi,
I worked as a lab technician for a government agency. We help the Police, Road Transport Department to determine whether the engine and chassis numbers of stolen vehicle are tampered with or not. My problem is that I could not locate the engine number of the above two cars. Even after jacking up the car and examining from the bottom, I still could not locate the position of the engine number. I hope some of you out there could help me.

Thanks