Call them directly.
THIS IS AS EXPICIT AS I CAN GET:
On the lower CA there is a flex joint at the axle end, and a rubber bushing at the rear (body) end. The replace the ONLY RUBBER BUSHING on that lower CA, you need p/n RE3761 "Super-ride Assembly Large". To do both sides you need 2.
On the upper control arm there is a fork on the axle end that mounts to a bushing on the axle. This bushing is not offered through RE to my knowledge. On the rear (body) end of the upper CA there is a flex joint since you say you have the super flex kit. So you don't have any poly bushing replacements for the upper CA.
If you don't have the flex joint on the upper CA at the body end, and you have rubber, then you need the RE3760 "Super-ride assembly small". If you want to do both sides then you need 2.
Make sense?