Hi Dave, I can at least provide some clarifications for the sniper plate - you should glue it with E6000 after removing the screws. Once the plate is glued one, you would only use ABS paste to fill the holes. Sand, polish, and that should be it.
Regarding the thigh ammo pack, I would have to do some digging around here to see what others have done with SDS. I unfortunately don't have the time at the moment, but I'll try and find you some info shortly. Thanks!