Don't believe everything you were taught, the S&D never really closed in 1966 and indeed the switch to diesel traction was made. In the summer of 1975, class 40 40017 is seen heading towards Templecombe with 7 blue and grey mk1s in tow. S&D practices hadn't changed much; the disc code was still used by the footplate crews as a homage to the old S&D headcodes in steam days and the quirky S&D practices at Templecombe remained.
Seen here passing through Wyke Champflower:
Passing through Cole. The BR(S) nameboard was still in place at this time and you'd be hard pressed to spot any differences from steam days.
Approaching Templecombe before a wider shot of the train in the platform.
As we all sadly know, the S&D did in fact close in 1966 and no scheduled diesel services ever operated over the line (though a handful of DMU railtours did visit in the late 50s/early 60s). BR blue is not my cup of tea however the new BR Blue pack is excellent and I would highly recommend to anyone who does have an interest in that era. It's nice to see proper BR taillamps too instead of the modern lamps seen previously!
Cheers,
PLP