Hi Gerhard,
The term GSV (Generating Steam Van) applied to all vans which had both boilers, for steam heating, and generators, to provide electrical power to the train - sometimes called 'hotel power', not just the vans converted from ex-British Rail stock. Thus the Dutch Vans (3157-66*), the BR Vans (3171-76 and 3177-92) and three series of vans converted at Inchicore from earlier stock (3201-12**, 3213-18 and 3219-24**) were all classified as GSVs (* the Dutch Vans were originally delivered as steam heating vans and were later converted to GSVs; **3201-12 and 3219-24 also had passenger accommodation and were Brake Standard GSVs). The GSVs did indeed operate with coaching stock that was not fitted with dynamos or batteries. With the exception of the 113-class, CIÉ / IÉ locomotives are not fitted with train heating boilers. There was no difference it the type of stock that the various types of GSV operated with, though generally the 3201 and 3219 types were to be found on suburban services. This was not a technical consideration but rather a means of increasing train capacity by replacing a full van with one that had passenger accommodation. GSVs were used on trains during the summer months to provide power for lighting, catering cars (fridges etc.) and any other requirement for an electric supply. There was also the need to have a brake van on the train for parcels traffic, luggage, bikes etc and also to provide accommodation for the guard.
I don't think that the G-class ever ran with just one Craven coach. There would have had to have been a brake van on the train and this would have supplied heat and power to the coach. However, on the Loughrea branch the normal carriage used with the G-class locomotives was brake composite No. 1910 (Inchicore 1959). Power for lighting was supplied by batteries, charged by a belt-driven dynamo. Heating was provided in a novel way - a storage heater which was plugged into a socket fitted under the edge of the platform at Loughrea at night. They just had to remember to unplug it before the first departure in the morning!