Hi Roger,
I modified a couple of standard size Futaba 3151 servos into linear motion servos and imbedded them in the pylons. With a little reworking and shaving things down here and there they just fit. The conversion kit is inexpensive and is available from Tower or EMS.The bottom of the pylon has two small tabs that mate against matching tabs from the bomb. Each tab has an inline hole to accomodate a music wire being pushed through. The servo arm pushes the music wire through the tabs to hold the bomb, and pulls it to drop the bombs. The bombs are snugged up against the sway braces to stop them banging around.
Regards
Mike