I don't recall one (which is not to say it wasn't done). The 123s went from Cardiff to Old Oak/Oxford around 1969, and Minehead closed in 1971; we had moved away to the Wirral by then, but regularly visited back in school hols. There was a summer Saturday through train pretty much to the end, but I always recall it being a Hymek (which were themselves actually quite rare on the Berks & Hants, though normal again by Taunton), and would surely recollect any 123 coming through; earlier, when new, they did so for a couple of years on Cardiff-Plymouth. Though the signalling on the Minehead line was stripped right back to the minimum a few years before closure, a run-round loop at Minehead was always retained to the end. The diagram was out & back from Paddington, but crews changed at Taunton as the Old Oak sets did not sign the Minehead branch, and if the 123s were any way different to local dmus I'm not sure the crew would know them.