In the video you can clearly see the back end assembly and that heavy frame at the end of the main fuselage just aft of the RPB you can also see the HS being fitted followed by the rudder
https://www.youtube.com/watch?v=6OQigxFYIUg
BTW now realise those tubular parts are not the screw jack but have no idea what they are, there appears to be 4 lower and 4 upper, they may even be adjustable length like a turnbuckle, if so are they tensioning/strengthening devices for the frame to enable it to cope with loads from the HS, there are 2 vertical movent ones and two horizontal movement ones at top and bottom, it is hard to see the horizontal ones as they are gong forward and hidden by the structure, post 663 shows them from within the HS compartment looking aft.
looking at the left hand fuselage of the two, you can just make out the rear door , going aft as you get to the HS compartment the skin changes colur to a greyish shade, is thus the approx area of the RPB, trying to get a visual handle on the size of the HS compartment