Here's a pic taken inside Haymarket shed (early 60s I think). [The appalling condition of A4 No. 12 suggests to me that it was the last days of steam at Haymarket.]
I'm a bit puzzled by the loco at the L.H. side of the photo. I've tried to identify the class of the loco, and keep coming back to a Thompson B1 ~ except for one feature.
The 'front corner' of the running plate where it drops down towards the buffer beam has a rounded valance underneath, but on every photo of B1s that I've been able to find show that valance as having a sharp inside corner at that point.
(I hope I'm using the correct terminologies above, but a look at the photo should make it clear what I'm prattling on about )
The only pic I've found that has a similar feature is this one of a Piercy kit of "Springbok"
Were there one or two (or more) B1s built with that rounded valance ?
RCTS 2B tells us that in 1956 Cowlairs Works started increasing the radius of the corners as the engines passed through shops to solve the problem of the corner angle iron cracking and having to be rewelded. No other works did this so only Scottish and Carlisle based engines were done. It doesn't list what engines were treated except for mention of 61323/48 which were transferred to the Eastern Region in February 1957 and a photo of 61404. 61243 61344 61357 61402 & 61407 also appear in Yeadon's with the alteration.
Out of the list of numbers that you mentioned, only 61404 was ever a 'natural Haymarket loco', although by 1960 it had gone to Parkhead 65c and by '63 had come back east to St Margaret's 64a. There were always plenty 'foreign' locos at 64b (as I expect with most busy mainline sheds) so at least I can thank you for confirming my B1 suspicion.
In my opening post I said I had never found a pic of a B1 (with that curved valance) ~ well, while searching for something else I found THIS PIC of 61308 at Dalry Road.
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