Harry,I'm not sure of that, but I think you will have trouble finding the lock that fits your ignition key as a separate part.
Do you intend to fit in the original lock that was on your former gas cap?
Do you have only one key for the car (as it should be on a 71 280sl)?
Last year, I had my whole set of locks changed in order to have one single key for all.
SLS germany sells a complete set including the ignition switch, and the gas cap.
A bit pricey, though...higher than a chrome plating process,indeed, but it might be the only way of solving the key issue.
In my case, the gas cap was'nt the original one, but an awful plastic black...thing, coming from who knows where, and so I had no metaphysical question on throwing it away.
Philippe from Paris
'71 280SL manual 4sp