2005 was a single grid year. Engines could be 674cc carb (583 with the DP 680cc big-bore kit) or 618cc FI (Class A) ... although some decided to get the best of both and run 674cc FI engines
It's marked in Wiki as being "675" rather than 620 or 583.
It was 2006, the second year, that there was a split into the two classes as it was obvious that the bikes were not equal.