I emailed the guy in the link from the previous email and this is what he said.
Yeah the output shaft from my 06sti transmission does not fit the legacy spec b viscouss center diff that I have. Now I just have the viscouss center sitting on a shelf . I did this all on my 07 wrx, its a swap of course. I didn't even hook up the dccd because if you change it to 80/20 on the street you will just end up destroying your center diff. The dccd is for the tarmac only. I was told this by several subaru techs who had replaced customers dccds because they messed with it on ca's messed up roads. Hope this helps.
Looks like we wouldnt be able to do it even with a tail housing?