Magnesium alloy like that should be pretty easy to drill, probably softer than steel. You could either carefully drill holes for quiver inserts...just make the holes ever slightly smaller than the knurled part of the insert and then tap the inserts in making sure you do it straight, or if they won't grab/hole ever so slightly too large just epoxy them in. You could also just drill the holes and tap them directly, but I wouldnt if you thought you'd remove the quiver often, as the mag threads might not hold up to repeated use. A drill press or drill with a level or a real good eye could do this project. Use a small pilot bit and then work your way up, drill steady without heating up the bit.