Sulu up there looks great, he might be what you're looking for or at least the head. Looks like a 1999 Ken body which is a smidge taller than the usual non jointed ones.
My RAH is one of the earliest ones and the post of a screw sticks out from his body and the arms stick on that. There's nothing to hold the arms on to the body so they come off cleanly at certain angles. To get the head off if yours has screws in the back of the neck undo them, it's a dumb bell shaped piece holding the head on but it's easiest to keep that with the head. Any replacement will just need a dumb bell of it's own. Stick it in place and screw the neck back together.