I learned some lessons from magnetizing my first crone, and put those into practice in assembling the second crone. Because of an impending tournament I didn't finish most of the Harpy bits, but the arms themselves are simple to add to.
First up, was to leave the tail in halves and drill through the rear wing sockets.
These are the perfect size for 1/8" magnets. I clean it out until the magnets can slide in and out since the magnets on the wings will be mostly added to the end of the nubs, sliding into the cavity here. From there I used putty to build a bridge of sorts, and put another 1/8" magnet into the middle. This single magnet will be close enough and strong enough to hold the wings.
Meanwhile, I assembled the bottom half of the torso, drilling out pin-holes for the front wings (and on the end of the wing's front ball joint, where the pin is affixed), and then magnet sized holes for the weapon arms, again using the 1/8" magnets.
Once the weapon slot was drilled out, I added the magnet on the inside and held it in place with some more putty.
The final magnet was for the head, which was much easier with the neck plate not yet attached. For this part, it was a simple matter of holding the heads up to the neck plate, then drilling through from the back. The drill holes are then perfectly lined up, and then expanded them to hold 1/8" magnets.
Once the magnets on the body side were all in place, I could go ahead and assemble to body and tail all together and it is ready for paint.