hmm... I just finish reading the detail section for 135 installation kit. It seems like it is what Mr. 5 did with his install, where he send in his stock diff, have them separate the welded ring gear then send it back to him for install. So there might be a long down time involve.
Besides, HPA is doing this also, ~$2000 for the completely assembled Diff + 800 core charge. So there's no down time. Unless Wavetrac is offering a better pricing, I might just go with HPA.