Take a look on Real OEM for part numbers. I think Coupe + Roadster are different and M different again.
If you take a look at the springs the normal ones have a splodge of blue paint on them. The Sport springs have green paint on them (I think its that way round - been a while...)
If I were you I'd bite the bullet and buy a complete set of Eibachs for about £130 in Germany. They'll be with you in a couple of days. By the time you've got all your tools out etc. it'll only take you another 20 mins to do the other side (especially if you have someone to help). You could then sell the fronts or if there is a noticeable difference in height front to back swap them at your leisure and flog the old ones on ebay.