Stanier locomotives had a very strong family resemblance, and Black 5's & Jubilees were very similar, especially head-on. My money would go on the special working being a Black 5; at any event it's certainly not the Coronation class Pacific (for some reason we always referred to them as "Semis" in my locospotting days.....)
Lord, I spent some time at the railside in the 50s and early 60s- New Street, of course, and Snow Hill - now that was a lovely station before "rationalisation" - occasionally Moor St, most frequently my local stations at Duddeston & Saltley, sometimes Aston and now and then, when finances would stretch to it, a day out at Tamworth Low Level, where we used to thrill to the passage of Princesses & Coronations at full chat, and where I saw both the prototype "Deltic" in its pale blue livery and the LMS diesel pair 10000 and 10001. Does anyone remember the old Blue Pullman, by the way? Probably the forerunner of today's HST....
Graham