For now, I am using modified stock EVO8 rear dampers (KYB) with cut 7 passenger van springs. These springs started out 450 lbs/in (8kg/mm) and are now around 600 lbs/in (10.7 kg/mm).
To see required mods to fit EVO8 on the van (or 1g DSM or Galant VR4), see my CarDomain.com page (www.reitmanracing.com and choose my Summit)
But this rear suspension is very much "work in progress", so I will likely change it.