Hi, Ken G:

Buy, beg, or borrow Sander and Brown' book "The Philosopy of Vacuum" and read chapter one - Einstein's 1924 paper "On the Ether". See if you can keep the book for a while, so you can refer to that chapter after reviewing my model of quantum gravitation on ATM. By the 1920's Einstein was trying to get beyond the mathematical model of "space-time-curvature" and determine just what was being distorted by the presence of matter. He needed a dynamical ether that could be conditioned by the matter and energy embedded in it, and it also had to be responsible for the transmission of EM waves through space.

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The ether of general relativity therefore differs from that of classical mechanics or the special theory of relativity respectively, in so far as it is not 'absolute', but is determined in its locally variable properties by ponderable matter.

Albert Einstein, "On the Ether", 1924