I think you have the right event ropat (Ormond-Daytona, January 30, 1904), but Gerd says he had never heard of the mystery driver, and I think that he would certainly know "Willy K.". There were several Mercedes cars at this meet. This car looks smaller, so I'll try: James C. Breeze on his 40 horse power Mercedes racer.
Edit: I have just discovered that Breeze (Breese?) was not entered in the 50 mile event, so I'll try: H. L. Bowden with his Mercedes 60 hp (he took second to Willy K).