Yes, the number is what I have. You have an extremely rare wagon plate too! Only four of these brake vans were ever built, by the LMS at their Earlstown wagon works in 1944. Although they were an RCH design, as a post-war standard brake van. Despite their design, they were issued with an LMS diagram (2046 if my memory is correct). Each one was delivered to the LMS, LNER, GWR, and SR. Further details can be found in Bob Essery's excellent LMS Wagons - the definitive reference on the subject. I've no idea what happened to the other three vehicles - be nice if one turned up on one of the preserved lines and was renumbered and re-united with 26500.
Another point worth mentioning from the modelling standpoint is the storage of brake vans in connection with the Quayside branch. The short siding at the extreme eastern end of the grain dock, viz., the stub in Trafalgar South yard on the south side of the two lines through to Red Barns, was used predominantly as a holding point for brake vans. Generally there would be at least three brake vans there. My mother mentioned playing on them in the 1930's so it must have been a long established practice. Furthermore, the platform adjacent to this stub siding was a builders merchant yard with stacks of roof slates, chimney pots, timber window frames, glass and so on. Just another piece of information for modelling authenticity. I dare say these will be quite a challenge to represent in 4mm scale.
Bill Donald
Dublin, Ireland.