Last weekend my brother picked up a Watsonian 'Silk' chassis and a Busmar (I think) chassis - it's the one with the two parallel flat bars that the fittings can slide up and down before clamping into place.
He bought two chassis to get his hands on the associated pile of fittings.
He's being cagey about his plans, but if it's half as good as the Briggs he restored it will be worth seeing.
GC