I'm presently working from a list of coaches wired as AEC trailers, which is given in 'Diesel Dawn' (Flanagan) and is credited to Colin Holliday. I suspect the list may have been based on the CIE carriage register - flange lubricator has a copy of the 1969 register (with annotations to update it to the mid-70s) which I hope to cross-reference with the list in 'Diesel Dawn'. I think the lists are accurate for 1969 but may not be complete for the 1950s - for example 1907 is not included (it appears to have lost its control equipment in the 1960s) and diner 343 is not included (because it would have been scrapped before 1969).
Anyway, at present the list in 'Diesel Dawn' and photos are the best information available to me. The list includes only three GSWR normal passenger vehicles wired to work with railcars. All are corridor seconds (which would have been corridor thirds before 1956), numbers 1300, 1301, 1308. There was also a variety of old GSWR catering cars, plus one DSER.
GSR normal passenger vehicles through-wired are the batch of suburban non-gangwayed open seconds (ex-thirds) 1331-1334, and suburban non-corridor compartment composites 2111-2113. Again there were a couple of GSR catering cars through-wired too.
Of course it's possible that there were more old vehicles through-wired which haven't made the list, perhaps including corridor composites. Most of the photos that show GSWR corridor stock in railcar sets seem to be of the corridor side, which was very similar on both the seconds (ex-thirds) and composites.