Up for sale on ebay UK at the mo courtesy of Paul Milner is this rather wonderful and unusual Tynesider pillion seat. The Tynesider is for sidesaddle riding and surely can only really have been intended to use with a combination. The mini chesterfield style is charming and puts Goldwings to shame!
The fitting seems to be on a pillar rather than rack but due to the weight it would seem that more than one mounting point would be wise.. It's not cheap but try an find another: museum piece is a phrase often banded around but here it is certainly true. You've still got a week to bid here at time of writing.
There's nothing out there about the Tynesider but Occhiolungo has an article on veteran era pillions.