Silver Surfer,
Check out Wikipedia for the history of the W113, and "The Original Mercedes SL-Restorer's Guide to the SL's" by Lawrence Meredith covers this very well. Initially, the 230 was fitted with Michelin X radial tyres, however due to less than acceptable performance, Firestone-Phoenix and Continental radials were the most common OEM replacements. Also, according to the Guide, Dunlop's were used for cars going to England. So, in short, all are correct. There is also some wonderful information and pictures in "Factory Original Mercedes SL" by James Taylor.