Here's a view of what we're trying to do. The pin lets the waist rotate while the axle lets us slide the torso up and down.

•The bushing has lips on both ends, modify the crotch's hole to clamp around the bushing, letting the lip anchor it in there. Remember to keep things more-or-less centered. You can glue or weld the bushing solidly in there, it doesn't need to rotate.

•The pin connector I had was too long, so I simply cut it down to the right size, making sure it could still securely accept the pin. Then just shove it in the ab hole.

•Test fit to make sure you get a flush fit. The great thing about the axle is that it lets the torso slide up and down. Once everything looks good, glue the connector in there.

Here's what it looks like. The pin is what lets everything swivel.

The swivel action will be loose because the pin is smooth. To stiffen it, take the pin out and smear a little bit of super glue on the sides. Let it completely harden. Then pop it back in and see if it's as tight as you want.

(Alternately, you can use a black LEGO Technic pin with friction ridges, and replace the bushing with another pin connector.)

There you go, done.

Rawr.