He was still reluctant to divulge such secrets even when asked on those Blu Ray commentaries. The old Criterion LD of Jason and the Argonauts did go into how a sword held by an actor seamlessly blends into the one thrust into the Hydra's neck.
I sincerely hope the studios release the rest of his films on Blu Ray. I haven't seen Valley of Gwangi or Beast from 20,000 Fathoms in a long time.
TCM ought to do a tribute. They premiered the fairytale short The Tortoise and the Hare, which Ray had abandoned when his Hollywood career took off. It was completed by some fellow animators and fans 50 years later!
Part 1
http://www.youtube.com/watch?v=SoGQDGMn_Lo
Part 2