Hi Robbin,
It is not really a big deal obtaining the VIN number or the ID plate.
Firstly, the VIN nr is stamped on the RH 'chassis rail', between the RH spring mount and the air filter, under the throttle body is a stamped number starting with 113. Google Pagoda Vin number location or chassis number location.
Secondly, confirm this number with the registration documentation. Apply for a VIN number certificate from Mercedes Benz.
Thirdly use this documentation to order a new ID plate. There is a chap on this forum who makes a perfect copy of the plate, provided your can supply the correct documentation.
I have just gone through the process and I am extreamely pleased with the certificate from Mercedes as well as the new plate.
As far as the cut out in the firewall pad. I believe some cars did not have the said ID plate, depending on where it was exported to. Some countries had different requirements. I am sure someone will be able to answer your question.
Regards
Chris