Re: "could lead to a young universe with a young Earth and a young fossil record"
The currently-accepted age of the Universe is 13.7 billion years. The age of the Earth is given to be 4.5 billion years. The Earth thus came about in the last third of this Universe's current existence.
If the speed of light was different in the early days of the Universe, it might indeed mean that the Universe could be younger than is currently accepted, but I doubt that would change its age by 50%. It would likely be a lot less than that, if we can find a way to prove anything.
As far as the age of the Earth is concerned, nothing about the speed of light will change anything because the age of Earth's crust is not determined by light but by the degradation of uranium into lead which is a fixed constant. So no, whatever happens to the age of the Universe, the Creationists are not going to be able to twist that into a 6,000-year-old Earth.