For inserting the brass screw mounts, I found the best way was to partially screw them onto the longer of the available screws and then hold them with needle nose pliers while briefly heating them with a mini jet flame torch. The pliers grip the screws very well by sticking one tip into the hex hole of the screw (see the photo.) After three seconds of heating in the flame, the brass mount is hot enough to melt into the plastic, so insert it until the top of it is flush with the mounting hole. Then release the grip of the pliers and adjust the angle of the screw that's sticking out so it's straight in all directions. The plastic is soft, so the brass and screw might move slightly by gravity. In a few seconds, the plastic will quickly harden. Remember, the screw is still hot at this point, so don't touch it with your fingers to move it. Until it cools, use the needle nose pliers to adjust the angle of the screw.
I hope this helps. Please feel free to use this post thread to add any additional tips you think others might use.
Thanks!