GWR 45XX class 2-6-2T No 4549 waits to leave Barmouth with a train for Oswestry in c1938.

Gwyn Briwnant Jones in his book Talerddig in Great Western Days gives an in-depth write-up regarding a Sunday excursion that went from Barmouth and Aberystwyth to Birmingham Snow Hill via Oswestry. I can't find any service trains from Barmouth to Oswestry in 1938. However, what is intriguing these Sunday service trains were meant to augment the Saturday through services rather than provide day excursions. An indication of a single lamp on this train might enforce the argument that this and the aforementioned services are one of the same. I'll include GB Jones, write up for your interest. "Up to 1932, the only Sunday services were the two mail trains, one each direction, between Whitchurch and Aberystwyth, together with their coast connections between Machynlleth and Barmouth. Then, in 1933, a new train appeared between Birmingham Aberystwyth and Barmouth. Departure from Snow Hill was at 10.45 am and the route chosen was via Oswestry as presumably the signal boxes along that corridor had already been opened for the passage of the mail. After a five minute halt at Oswestry, the train left at 12.41 pm,, and stopped at Welshpool and Newtown for a minute's respite at each station, before reaching Machynlleth and 2.18 pm Here the train was divided; Aberystwyth passengers reached the coast at 3.00 pm; those bound for Barmouth had all reached their destination by 3.28 pm. A Corresponding 'up' service left Barmouth at 2.50 pm - the two coast 'crossing' at Llwyngwril. The mainline service left Aberystwyth at 3.30 pm". They were successful for they appeared up until 1939 but were not reinstated after the war.
Photo: Rail Archive Stephenson