"Again there was a little delay, awaiting the train from Llanidloes (says our chronicler), and it was half-past three o'clock before The Train of the day fairly started. Filling the carriages and trucks was no joke. Admirable arrangements had been made, and the ladies were first accommodated with seats. One or two gentlemen did attempt to take their place before this arrangement was fully carried out, but they were very unceremoniously brought out again, amidst the ironical cheers of the outsiders. At last the forty-eight trucks and carriages were loaded, and, at a moderate estimate, we should say, 3,000 people were in the train. The two new engines, The Llewelyn and The Milford, [shown below] were attached to the carriages, and were driven by Mr. T. D. Roberts and Mr. T. E. Minshall.*

"Although the train was so heavily laden with passengers, there was a large crowd of people left to cheer as it slowly passed out of the Station. The appearance of this monster train was magnificent. More than 2,000 of the passengers were in open trucks, and at certain points, where there was a curve in the line, and a good sight could be obtained, the train, as it wound its way through the valley, presented a scene not easily to be erased from the memory."

* The song - written before the event - says that "Henry lad shall drive" which does not accord with the names given in the report

References:
Gasguoine, C. P. The Story of the Cambrian: A Biography of a Railway.: (Wrexham and Oswestry, Woodall, Minshall, Thomas & Co, 1922) pp. 23-24
Image of the Milford http://newtowntextilemuseum.co.uk/resources/History_articles/Newtown%20to%20Llanidloes%20Railway.pdf (accessed 06Feb21)