Bob,
During the 230SL, 250SL, and maybe some 280SL production, there was an ID plate rivited to the firewall, near the windshield, on the right side of the car. This had the VIN as well as other info. On most 280SL cars, it will be located on the driver's door frame. The VIN is also stamped on the right frame rail. This is hard to see, but it's on the top surface of the frame rail under the Venturi unit (where the big air hose connects to the intake manifold). Finally, on the left side of the engine bay, between the brake booster and the sub-frame mount, is another ID plate that has some 3-digit option codes as well as the last part of the VIN.
These cars also have engine numbers, transmission numbers, axle numbers, and steering assembly numbers that can be found on the data card and on the assemblies.
Happy Hunting!
Rodd
1966 230SL Euro
1994 E420