The locals on Salisbury-Exeter pretty much disappeared, but the few that remained were normal WR dmus.
Bristol to Weymouth, apart from the dmus (entirely in winter) was Class 31 and 47, gradually moving from the former to the latter over time.
Although Waterloo to Exeter theoretically changed over from Class 33 to Class 50, there were still a number of Class 33 around as substitutes, as I don't think there was a spare Class 50 kept east of Exeter. Occasionally they were turned out double-headed, which avoided delaying others on the single line.
If you have a Peak on your layout, these turned up from time to time at Bath Green Park right to the end of the S&D.
For the Evercreech-Burnham line, maybe a Wickham platelayers trolley with 4 passenger instead of ganger seats - because that is all the accommodation that ever seemed necessary on the branch trains
The Brighton-Exeter Hastings dmus were, what, 1970s-80s? Normally a 12-car formation, one with Buffet. Out from Brighton in the morning, back in the afternoon. I believe it worked ecs over from St Leonards depot to Brighton first, where some convoluted shunting was required as the formation was too long for the one platform at Brighton that connects to both east and west. It was certainly the noisiest train of the day, departing Axminster on full throttle all four engines to take a run up Honiton Bank westwards, although not quite as bad as when I once saw, and heard, two such trains depart from Tunbridge Wells in opposite directions at the same instant ...