"Will a 2006 Cadillac STS-Y. STSV 6 speed auto 6L80E will fit up to the LS1"
I have not seen anything that says it won't. Your problem is how are you going to control it? It has its own controller built in and the E38 ecm is the one that communicates to it. I am not sure if you would have to enlarge the transmission tunnel. There could now be some stand alone controllers on the market. You would have to reasearch it.