I now see the problem. If you look at cattle wagons from a Great Western point of view, you see that the GWR wagons have lettering S, M and L indicating the location of the movable partition. Obviously the lettering on both sides need to correspond. Hence it is no great leap of imagination to expect that the LNER size label would also correspond! But not the case it seems from expert research and observation.
The fine work done on the conversion and the resource on the three aspects of these wagons is truly rich. I thank the writers for such fine application. For my Wiltshire GWR layout set in the mid 1930s I was wanting a good smattering of foreign horseboxes, cattle wagons, and POs. These Oxford wagons, if the underframe is replaced to accomodate P4 and incorporating springing are quite attractive. As I'm getting on I frankly need a few short cuts, so with the cattle wagons might not switch one side around at all, as only one side will be viewed. It's a long shelf layout close to eye level.
Thanks again for the generous education, as I have no LNER archive.