Welcome to Flyertalk and welcome to the BA forum
Adam Georgeson, it's good to see you here and I hope that we will see more of you in the future. And I hope that you have a good flight even if the IFE is a museum piece.
The mid-J 747s are not all being updated with new IFE since they are destined to be taken out of service fairly soon. But the way to find out is to look on flightradar24 under your flight name the day before travel, this should give the aircraft registration. Then you can either use thebasource.com to see the IFE status, or alternatively have a look in this thread.
Mid-J 747 Cabin Refresh