Here's an update on the current state of this build...
I've replaced the AST dampers with JRZ RS-Pro dampers. The JRZ units have both compression and rebound adjustments and remote reservoirs.
I decided to match the new dampers with a new set of Swift springs (784 lb/in front, 560 lb/in rear). I also installed 45lb/in Swift helper springs in the front and 223 lb/in Swift assist springs in the rear. The helpers in the front are merely there to take up the slack between the main spring and the perch. In the rear I opted for a heavier assist spring which will provide a bit of mechanical force to keep the drive wheels in contact with the road when unloaded.
The biggest change with the new setup is that the rears are now a true coilover where the spring is mounted directly on the damper instead of the OE location of the control arm. This changes the motion ratio for the rear spring making it more efficient. In the stock location the effective rear spring rate is roughly half at the wheel vs the coilover setup where the wheel rate is essentially the same as the actual spring rate.
In order to install a coilover setup on the rear of the E89 chassis the damper needs to be inverted. I used the Turner Motorsports E46 upper mounts found here:
http://www.turnermotorsport.com/p-31...3-z4-pair.aspx along with the reinforcement kit
http://www.turnermotorsport.com/p-34...ement-kit.aspx
The only modification necessary to fit these mounts was to drill a new hole as the E46 mounts are 2-hole vs the 3-hole E89 mounts.
I also replaced the front and rear swaybar endlinks with fully adjustable versions from Turner Motorsports. The fronts are E9x fitment and the rears are E46 fitment.
I did the install myself at the Ratchet Head facility in Newton NH and it took about a day. Once the install was complete, we also did a corner balance and alignment.