Yes there was a big move from the LMR when it shut, including 6686, but 6686 was at Droxford before that with the rest of the Southern Loco Preservation Co's stuff - from memory 30064, 6686, the GW Toad brake and the SER 6w passenger brake....
I think that the photo was taken sometime between about 1975 and 1977 as I seem to recall that 6686 entered traffic about '74 or so and it is clearly coupled next to a Maunsell TO - 1309 did not eneter traffic until late 1983 and the photo looks too early for that, whilst 1365 was withdrawn in 1977 - so I think that dates the photo. It is clearly is C class 592 in the background, which moved to teh Bluebell in 1970.
Anyway getting back onto the thread, I must say that I would be a little dissapointed if the Hornby choices are too skewed by the push pull sets - if any group of Southern coaches are over-emphasised it is Sets 600-619. These Maunsell pushpull sets were only in service for about 5 years, but because a lot of photographers were active then photographing the diminishing Southern branches, people seem to think that these were the typical Southern push pull sets. I think that that the, much longer serving, sets that these replaced (and in frequently operated alongside) would be much more worthy targets: things like the converted ex-LSW ironclads, the ex-SEC birdcage vehicles (without birdcages) of course, the ex-LSW gate stock, the ex-LBSC units and the ex-Isle of Sheppy railmotor vehicles would all have been far more interesting and relevant to a much longer period for modellers. What I am concerned about is that if the choice of vehicles by Hornby precludes typical Maunsell mainline/secondary route/branch formations, which is far more relevant - if we get a BCK, TO, BTK and a CK then we can do quite a lot, if not we cannot .