Apart from the ex-IKB part, Mainly Trains also have a 6' spring, MT119.
My photos of the Didcot G20 are mostly of the underside but one definitely shows a parition. Indeed the external appearance of G20 would suggest that it is a double saloon. They were third class saloons, and Harris says on p44
"Fifty-four three-centre roof, six-wheel third saloons were built to two diagrams from 1892-98. They had two open saloons divided centrally by a lavatory and WC, and all seem to have been withdrawn by the 1920s"
The other diagram was G19.
Nick