You need to find the appropriate .edm name of the dispenser unit and the weapon you want to use. Then declare a loadout in the lua. The loadout delaration will need the appropriate data filled in such as names, CLSID, weights, number of elements, position of the elements on the dispenser, etc. After that is done you need to place the loadout information under the pylons details you want to have the weapons mounted on.
Sometimes there is already a CLSID listed in the aircraft lua and that will save you the trouble of declaring a loadout. One picture is a Thud during load testing, the other is the VSN F-105 (coincidently, also during load testing)
Information is being sent to the VSN team on what I did to load up the M117's on their fantastic mod.
seabat