It’s enough to make your head hurt!
Well, you kicked it off
There was a transfer of lines south of the Westbury-Taunton line in the 1950s to the Southern, which was reversed (and then some) in 1962. Didn't seem to make much difference to operations at all, but any items needing to be replaced were done Southern-style. The replacement footbridge at Maiden Newton, on the Weymouth line (still there), was another example, being Exmouth Junction concrete works' prefabricated finest ...
Locos on the Taunton-Yeovil line were supplied from both ends, the closure of the WR shed at Pen Mill and transfer of locos and turns to the Southern shed at Yeovil Town was one of the more significant changes, but the loco types remained and the Town shed commonly thereafter had half of each constituent's stock. Normally WR locos were used to Taunton, but from time to time an SR loco, I never saw anything Southern other than an N 2-6-0 class, and more often than not it was 31840 for some reason, come to Taunton. Green SR stock likewise did maybe one trip a day. On summer Saturdays, to avoid congestion by shunting across the main line layout at Taunton, the Southern N, plus stock, was commonly backed into the Taunton Down bay and did the next departure onwards to Barnstaple, the Southern getting their loco (all of which were officially allocated to Exmouth Junction anyway) back there.
The half-dozen Taunton to Yeovil trains towards the end were characterised by each train potentially being headed by a different class. I never saw a diesel on the line, either dmu or loco, but have seen several photos of a D63xx on it.
Yeovil Town shed was an oddball, accessed from the Down platform of the station (just like Taunton), for almost all of its Southern turns were east and west up on the main line, several miles away at the Junction, so there was a steady parade of light engines back and forth. It always came as a surprise to find Unmodified Light Pacifics, often more than one, on shed at this little outpost.