The book referred to shows that, at the time of preparation, the last of the 1952 Earlestown-built special cattle vans had yet to be withdrawn, and it certainly looks like one. Although the 3-part version of the book was published in 1991-on, the original single volume was published in 1970 and presumably based on data extracted in 1968 or 69. I remember an immaculate one in a bay at Aberdeen in 1968, presumably waiting for an Aberdeen Angus bull.John Palmer wrote: The layout of the vehicle's cattle and attendant's compartments is very similar to that of the LMS prize cattle van to Diag. 1876. However, the data I have from Essery & Jenkinson's 'LMS Coaches - An illustrated history' is that all the LMS-built cattle vans were extinct by 3/65. That would leave lot 1638 to Diag. 1877 built at Earlestown in 1952 (surprise!) as a contender for the vehicle shown.
It's also maybe worth pointing out that Earlestown also built LNER design horseboxes in 1954-5, and these were allocated LMS-series diagram and lot numbers but numbered in the LNER series. It seems that when passenger stock was built by BR to a pre-nationalisation design the 'parent' company's diagram, lot, and the running numbers were used, but for freight stock all stock built by BR got BR series numbers. An extreme example of the latter was the NER design wooden underframe, wooden bodied 13t coal hopper built to diag 1/140 in lot 2050, B400200-B400499. Reverting to the Earlestown horseboxes, they had E suffix (ER maintenance) but were not solely allocated to the LM - were any on the ER?