Hey rog,
The QF SPs had C2 engines. The D4s were over the thrust limit certified. It actually gave QF a place to hang D4s which were getting a bit tired and could no longer make the D4 spec.
Originally the WLG operation forbade any derate or assumed temp operation so all T/O was full thrust. Imagine keeping the beast under control when your initial altitude limit was 3,000ft and you had a light SP??? Exciting!!! Flap limit speeds were a challenge.
One very frisky aircraft even at high TOW. The fuel feed configs at max TOW were simply a nightmare for the FEO.