Amazing coincidence.
I followed the photo link above, and then scrolled on through the string of interesting old colour photos there. Came to a 1967 shot of two Stanier 2-6-4T locos on an enthusiasts special.
Now I youthfully recall, on a holiday weekend in the 1960s when we had moved from Somerset to The Wirral, taking the electric train with the family from the West Kirby line into Liverpool. At Bidston, in the sidings along the station, were two Stanier 2-6-4T coupled, never saw anything like that there before or after. As it was a bank holiday, I presumed it was some holiday excursion from the Wrexham line to New Brighton.
Fast forward 55 years to today, and I see that the photo is of an RCTS railtour - at Wrexham. Over to Six Bells Junction with old railtour details, and I find it is indeed Saturday 29 April 1967, when the following Monday was the May Day bank holiday, and these two locos had come off at Bidston.
Here's the detail. Shame I don't still have my 1967 Ian Allan book to underline them both

. And it was certainly an Unusual Steam Loco Combination for there, so perfectly suits this thread.
Picture :
LMS Stanier 2-6-4Ts 42616 and 42647 at Wrexham Central station in spring 1967, with the R.C.T.S. 'Wrexham, Mold & Connah's Quay Railway Rail Tour'. 42616 was withdrawn in October 1967, and scrapped in March 1968, and 42647 was withdrawn soon after this phpto was taken, in May 1967, and scrapped...
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Six Bells Junction :