> I've not found anything about the stones being used
> by the racecourse myself - I'm willing to believe it, but
> that doesn't mean they weren't recycled from a prehistoric
> use?

It wouldn't be the first time prehistoric stones had been used for a horse racing course.

eg. Cerrig Llwydion in Ceredigion
http://www.themodernantiquarian.com/site/2657

K x