The motive power is easy to predict - It'll be either the Silver Jubilee 67, 67026, or one of the two Royal claret liveried locos, 67005 or 67006. No doubt both if there is a need for the train to be top and tailed for stabling purposes.
The Royal Trains is made up of a mix of converted (or in a small number of cases, purpose built) mark 2 and mark 3 vehicles that will certainly include the Queen's Saloon 2903, formerly prototype HST First Open 11001.
The remainder of the Royal Train stock is as follows:
2904 - The Duke of Edinburgh's Saloon - Previously prototype HST TSO 12001
2915 - Household sleeping car - Mark 3 sleeping car
2916 - The Prince of Wales' dining car - Converted from HST mark 3 restaurant/kitchen vehicle 40512.
2917 - Royal Kitchen/Household dining car - Converted from HST mark 3 restaurant/kitchen vehicle 40514.
2918 - Royak Household car - Converted from HST mark 3 restaurant/kitchen vehicle 40515
2919 - Royal Household car - Converted from HST mark 3 restaurant/kitchen vehicle 40518
2920 - Royal Household couchette - Converted from mark 2B BFK 14109.
2921 - Royal Household couchette - Converted from mark 2B BFK 14107.
2922 - The Prince of Wales' Sleeping Car - Purpose built mark 3 vehicle.
2923 - Royal Saloon - Purpose built mark 3 vehicle.
The platform that it is due to arrive into on the day will be apparent as the one with a red carpet laid out