"How can I find the chassis number on my Merc 93 280E? There's a whole
swag of numbers on a plate by the radiator, is the number here? "

It should be the first 3 digits of the VIN number.  At least that's how
it is on a 300SD.  The VIN number is usually on a tag visible through
the windshield, it's on the title, and it;s on your registration.