A/c are only usually confirmed the day before departure but could change even after that subject to operational requirements.
Out of LGW, you have a fairly limited choice. It will be a 744, either one of the 5 Alitalia built a/c (ROS/ROY/ROM/GAL/LIP), or one of the 3 former LHR a/c (AST/TOP/XLG). All are pretty much the same inside except the ex-LHR a/c have a better IFE system than the others.
