The last GWR AWS ramps seem to have removed in 1979, the same year that the HST started working two or three return workings to Plymouth and Penzance. (Or maybe it was January 1980 that they started).
Peaks had started working west of Bristol from the late 1960s as the hydraulics were withdrawn, firstly on passenger from Birmingham etc, then on freight and general WR internal services. The non-WR ones did not have the GWR AWS.
There was a fatal accident at Bridgwater in 1974, to an LMR Peak (No. 125), after which (I think with union pressure) every effort was made to use locos fitted with GWR AWS west of Bristol, which for Peaks was most (all?) of the Class 46, and Nos. D33-42, which from new had been allocated to Bristol Bath Road depot. A lot of Class 46 had been transferred to Laira as substitutes for the hydraulics, but the accident train, a Birmingham to Plymouth overnight freight, was running with a Class 45. The accident report, which came out the following year, lists the surprising amount of line which still had the GWR system at the time, although most WR allocated stock had been changed to dual system. Not those from other regions however. Disappointingly the accident report seems to home in on other aspects, and minimise the AWS issue, apart of course from saying that if it had been fitted the accident would be unlikely to have happened. In the main part of the report it says blandly that the line was fitted with "WRAWS" (which any WR man still called ATC at the time), and then several pages on that the loco was fitted with "BRAWS", it is left to the reader to notice the difference and make their conclusions.
As a onetime Southern question, they would have been used as general purpose Exeter locos, in particular heavy works and ballast trains beyond a Class 25, on any former Southern lines where they were not banned by virtue of weight or curving ability,. The latter is sometimes quoted as an issue for the 1Co-Co1 diesels, but if a GWR 28xx would go round, so would a Peak.