Thank you all for the amazingly swift and detailed responses! And @
trebor79 you might be quite right that we don't need an alarm and are awake all the way from at least GLQ or Dalmuir anyway...
But for the eventuality that we don't wake up by ourselves, I'll probably set a first alarm for 6.20ish for a first pre-breakfast glimpse of the Clyde from the room, and then a second/backup alarm a bit later to get showered and into the lounge car for Loch Lomond at the latest. There'll be enough opportunities for a sleep in later in these holidays!
Thanks again