Yes, I remember that as well but I don't have a reference either. If Stonehenge was brought from elsewhere then the fact that the area it now occupies corresponds (closely) to the area at the top of Silbury, it leads to the not unreasonable conclusion (taking in other factors as well*) that that's where Stonehenge came from (unless those particular dimensions held some special meaning to prehistoric builders, in which case other examples might be found elsewhere).

The idea that Stonehenge, or a Stonehenge-type structure, once occupied the top of Silbury is not as wild as it might seem - there are examples from other parts of the world of temples, even whole cities, being dismantled and then reassembled elsewhere, or old structures being deserted and new, similar structures being built elsewhere.

* http://www.eternalidol.com/ “What I give form to in daylight is only one per cent of what I have seen in darkness.”