... when using original calipers?

I can't remember for sure but assume the original front discs were solid?

I'm looking at buying some vented discs (with internal fins, not grooved, drilled etc) from Ferodo:
http://www.opieoils.co.uk/p-69775-fe...le-vented.aspx

It says compatible with Williams, but in other forums, for other cars, it says new calipers are needed when using vented discs, but doesn't explain why.

Anyone know if I can just fit these to my car without further modification please?