let the custom armor extend model biped and then add in the render method something like:
@Override
public void render(Entity entity, float f, float f1, float f2, float f3, float f4, float f5)
{
super.render(entity, f, f1, f2, f3, f4, f5);
setRotationAngles(f, f1, f2, f3, f4, f5, entity);
bipedHead.addChild(insertHeadarmorhere);
bipedBody.addChild(insertBodyarmorhere);
//etc.. to lazy to write the rest
}
hope this helps you - or someone else...
basicly this syncs your Model with the movements of the bipedBody (the Player)