This Selmer Zodiac is no museum piece with non-original McKenzie speakers (originally Celestions), missing/non-original knobs, missing sections of cabinet, no footswitch for tremolo (amp tech who last serviced it assures me the tremolo functions) but it looks and sounds great! More original examples are online for £1,500+.
Here is what the vintagehofner (good info on Selmers) website say...
'The change from "Crocodile" came during the last months of 1965, when Selmer moved totally away from two-tone cabinet coverings, and adopted an all black cabinet. The fronts of the units were livened up with a smart blue/black grill cloth, with distinctive "sine-wave" pattern woven in. The new amps were introduced at the British Music Trade Fair in September 1965.
The control panels of the Big Twins were now situated on the front of the amp instead of on the top as with previous versions. Less noticeable in the Twins was the incorporation of the power-amp sections with the pre-amp in the top chassis, resulting in the name given to these new amps by Selmer employees - "The Upside-Down" amps.'