I need a plain radiator cap, one which just seal on the top rim, and has no pressure relief assy, so the normal overflow can be used to vent to a header tank.

I know they exist cos one of the cars I used to own had one on the rad, took me a while to understand how it worked, I think it was a 2.8i Capri but not sure, can anyone help with a source, so I have half a chance of asking for the right thing at the factors.
Cheers.
Pete.

The old Austin/Morris 1300s had a blanking cap on the rad and a pressure cap on the expansion tank

Fantastic, thanks, even found one on the bay

burtons do them