Except for one little point. If the velocity of light were "wrong" by more than a tiny tiny amount (< .000000001 or so) the stars wouldn't shine and fusion and fission bombs wouldn't work. e=mc2. Energy equals mass times the speed of light squared. Since stars evidently DID shine through hydrogen fusion a billion years, plus or minus an eon or two, after the creation of the universe, and did so in a manner extremely similiar (identical as far as we can measure) to how stars fuse hydrogen today there can be little doubt that c2 (speed of light squared) is the same now as it was then.
I don't doubt that c was different at a time < 300,000 years after creation because the universe, had yet to become transparent, and was so hot that protons and neutrons didn't exists and all 4 forces (gravity, weak nuclear, strong nuclear and electro-magnetic) were combined as one force.
See Unified Field Theory and Grand Unified Field Theory, String and Super-string Theory. Read Stephen Hawkings' "A Brief History of Time" and Micheo Kaku's "Beyond Einstein: The Cosmic Quest for the Theory of the Universe" and "Hyperspace: A Scientific Odyssey Through Parallel Universes, Time Warps, and the Tenth Dimension". Absolute great stuff.