I can't recall, did the Paddington service reverse at Exeter St Davids, or did it run from Castle Cary via Yeovil to avoid doing so - or did it do different things in different years.
The climb up from Ilfracombe to Mortehoe was indeed stiff, and I wonder what happened in the rain when it was single line at the end if they couldn't make it. There was in the 1960s normally a D63xx in the yard at Barnstaple, but did it even have a crew on Saturdays? I only did Ilfracombe (twice) in a dmu, which was about 20mph flat out on the way up, with a handful of passengers, plus several minutes standing at Mortehoe, as they were still using steam timings, which must have been slower still. One of the advantages of the Hymeks with one engine was all the wheels were effectively coupled, whereas Warships with two engines and transmissions were notably prone to the front bogie slipping, even starting from Taunton station on the level on a wet day.