I dont know if you'll have any problems with the rear conversion or not but on mine I followed the directions to a "T" and my rear dogbones where about to fall out and looking from the rear my tires looked like this----> /-----\. I first thought I had something backwards so I switched everything around but still had the same results. The instructions stated that there should be 2 threads showing after you have the pivot balls screwed into the lower arms if using the hyper rims which I am. I ended up having to cut 3mm off the pivot ball stud so I could screw them into the arms without damaging the arms. I used my old arms and adjusted the new PBS suspension to match them and everything looks good. I've not started the front yet, I hope I dont have as much troubler with it as I did the rear. That Hyper .21 looks good.... Let me know how it works out for you, I might try one out...