a little further research, the USA Eibach website stating the same part number for 2004 Crossfire and SLK which is 2552.140

However, on the german eibach website (http://www.eibach.de)
2004 Crossfire
part number: 10-28-009-01-22
front axle load 1000 kg
rear axle load 890 kg

SLK(R170)
SLK 200
part number: 10-25-003-01-22
stamping: EW 2552001 VA
EW 2552002 HA
front axle load 815 kg
rear axle load 810 kg

SLK 200K, 230K, 320
part number: 2552.140
front axle load 845 kg
rear axle load 820 kg


So the quest continues.......