The orginal 12X was the Euro version (Corally front end, Corally wheels/axle unit more slots in chassis), then the 12X US version (Corally front end, US wheels/diff unit/ less slots in chassis) and then the WC version which uses the US wheels on an Associated front end (plus a t-shirt in the box!)
They then brough out a LiPo conversion chassis that still uses the 12x platform, but puts the LiPo on either side of the t-bar.
Corally USA have released a LiPo Link chassis which uses the pod from the 12X, this is a great car and is the one I am using myself at the moment!
Lastly, Corally are just about to release their own LiPo link car which should be out anytime now.
Hope that helpd a little!
Cheers!