Thanks Andy and Stephen,
As Stephen correctly said above,they were a common single fleet,
In later years while working the Ballina branch train we always preferred GSV 3173 as it was a comfortable and quiet van with a reliable generator and boiler and with the guards compartment at one end of the coach it was useful and not in the middle next to the noisy generator like the rest of the fleet,
3172,3173,3185,3177,3180,3184,3187 and 3189 were some of the best GSVs to work as they were in good condition-with 3173 and 3185 being recommended to the RPSI for preservation after withdrawal from IE service.