This post has been edited. If you already read it, additional information has been added that may cause you to rethink using this method.
The metal used to make this figures is extremely soft and brittle. You MUST use soft jaws. I will post about them in a bit. These are rubber jaws that slip onto your vice. But even then, you need just the right tension to hold the piece and not enough to collapse the die cast. The drilling is the easy part. Its the tapping that has the potential to wreak havoc on the die cast.
But I must stress that this is a last resort. These figures are EXTREMELY brittle. This makes them VERY hard to hold onto. There is a very real possibility that the cast can crack at any time while drilling or tapping.
In fact just taking them apart can cause them to break. After years of being stuck together, the die cast body alignment pins can get 'cemented' in to the mating holes and when you try to pry the 2 chest halves apart, they could rip off and stay stuck in the holes or I have seen several where the pelvis gets stuck to the 2 chest halves and working that loose causes the chest pieces to fall apart. Once you have a flaw in the die cast its like a crack in a windshield. If you take your knuckle and tap on the windshield you can expand and lengthen the crack. Well once the die cast has an exposed flaw, this compromises the strength of the surrounding material. And any pressure, like say from a tap or the tightening of a screw could be all it takes to collapse the die cast.
It can be done...Its very tricky...and unless you plan to throw the figure away, use this as a last resort to fixing vintage die cast figures.
I am going to look into the possibility of maybe using DEVCON to help strengthen the area around the hole.
Devcon (I believe that is a trade name) is liquid steel. When I worked in an automotive shop, we used it to patch motor decks and then they got surface ground. I want to see if maybe I can use it like a glue and let it dry around the screw. I would have to drill the hole a little larger, but it would alleviate the pressure applied by the tapping and clamping and would be a much safer approach.