Well, it's not the "The tail is just the same tail from the 747-400" as You've increased height of the fuselage in that section, and by doing it You've also increased size of APU exhaust into a whole canyon.
And the actual proposals of the double-deck 747 had it bit different:
Some other (earlier) full-double-deck concepts of 747 had the upper deck literally for the full length (like on Your drawings), but they had also the horizontal stabilizer relatively higher (so the actual "height" of the fuselage in that section was similar to that on original 747's) - see more on Secretprojects.