Here's what the Classic Center said about key blanks for my 230. They are the one-sided version so you will have to check for your 280. Hope this helps:
111 462 01 32 9604 ignition sug. list $ 16.50
000 766 20 06 9302 trunk & glove sug. list $ 36.50
000 766 19 06 9401 door & tank sug. list $ 36.50
Please contact your local Mercedes Benz authorized dealer for purchase.
Proof of ownership and chassis number required.
Regards,
Mercedes-Benz USA
Classic Parts Center
Kevin
Boca Raton, FL
1967 230 SL Automatic
670 Light Ivory
113 Bronze/Brown MB Tex