What the RAF did with the L1011's that fly to the Falklands now doesn't seem quite so odd.
The C2's (still more-or-less standard ex-Pan Am Tristar 500's inside) had the projectors etc. stripped out when they went military. Instead you are now offered a Sony Watchman and a list of available (fairly up-to-date) films.
Not sure how much a complete seat-back IFE set-up weighs, but this lot comes to about 700Kg's if I remember and is all stored in standard galley trolleys.