Dear Dr. Corda,
As I have not heard back from you, you either went to Croatia for a holiday, or my answers were too long or unclear. :) In case it happens to be the second, please allow me to clarify further.
1) Einstein's equivalence principle means that we cannot experimentally distinguish between acceleration and a *uniform* gravitational field. But no such *uniform* gravitational field exists in reality. That is, Einstein unrealistically ignored the *non-uniformity* of gravity, for even an arbitrarily small reference frame cannot ignore that non-uniformity according to Ohanian's paper.
2) The velocity of matter is c in *its* rest frame, and is spatially separated from antimatter by c(root-2) - the hypotenuse of Pythagoras' triangle. This 'absolute relationship' is consistent with Special Relativity, for if that matter is at rest relative to the observer we can ask how many seconds t' passes for antimatter if the observer counts t = 1 second, and the reciprocal of the time-dilation formula gives us t' = i. Clearly the 'absolute relationship' holds true even if that matter is not at rest relative to the observer.
3) If there is any uncertainty with respect to the position and momentum of matter, it will be due to the nature of matter, rather than *assuming* Heisenberg's uncertainty principle.
I hope that answers your questions. :)
All the best to you and your family,
Robert
