Grelland, the dirt-track set-up is far different from the U.K grass-astro set-up. Different springs, oil & pistons, camber links, even the amount of weight we are running. Check
http://www.2wdrc.com/tech/SetupSheets.htm for at least 5 set-ups from 2009 from Kinwald, Griffin, Sinclair, Sava, and Galan.
The first four are all U.S. dirt track set-ups, I think Eduardo's is for dirt with astro on the jumps.