I joined the RROC (Rolls Royce Owners Club) not too long ago, and so far I have never heard of a GM tranny in a Rolls. I have heard of GM conversions on the engines though.

A rebuilt Rolls engine using genuine parts and good mechanic can be $20,000 give or take a few grand. So for the people who want to drive a nice car and dont want to cough up the dough, they do a GM conversion for a cheaper price and cheaper maintence in the future. Although most people frown on this because a Rolls body with a GM engine just isnt original and hmm, I dont know how to describe it.