Hi minel - the config will be one of the LGW/MAN configs (there are 2, but they are almost identical), although which actual one and more specifically which a/c it will be, is not released for security reasons.
It's on an A343-300 as VS 57 is one of the extra BGI services over xmas, so will be 34 J / 35 W / 171 Y - Is showing as having 50 spare seats at the moment. Will be odyssey IFE, unless it's G-VSUN then will be V-Port. Have a good trip.