The scanner in the office is broken, so I can't scan any pics from the Japanese book right now... sorry for that.
The following may to some extent be useful, however, especially for you, saintmdn:
Regarding the hip joint, I found the enclosed picture from a statue of "Realm of the claw" Winstons team made after Small Soldiers. The hip joint is however parted like the feet joints of the soldiers in the movie and the shoulder joints of the Chip figure from Hasbro. This would be the simplest way, but in my opinion, a complete, closed round joint would look much much cooler. Any inputs from you guys regarding figures that might work as reference material? The same question applies to the connection of the chest/back and the belly. The belly is sunken into the chest/back part and posable to the front and back... but I have no clue as to how far the parts are stuck together and how they are connected. How about the head anyway connection to the neck anyway?
As already stated, the mechanism of the feet joint is the same as with the Terminator wrist as shown in the enclosed photo.
Furthermore, I think that it is safe to state the following: Judging by all the pics I have seen until now and the making of videos, there were two initial action figures which were thereafter amended in order to create the different characters. On one of the pics saintmdn has posted in his thread, Butch and Kip are shown. Both of them have resculpted chest and legs, i.e. underneath the grey clay, white resin lies in the form of a "plain vanilla leg".
In my opinion, the original arms of Kip, Chip, Nick and Link looked like the ones Link and Kip have (those two are actually exactly the same, as especially the green and red version of the fabric wrapped around their right arm show). For Nick and Chip, shirt sleeves were sculpted over these arms. The forearms are all the same (for Kip, Chip, Nick and Link that is and for Butch and Brick respectively). The gloves differ again. As already stated, the legs including boots of Nick and Link are the same as well, only in different colors.