The 737-200s with the twin toilets in the tail was the spec on the early aircraft and was also common across the BA and Sabena 737-200s (which later ended up with European Air Charter). The rear galley was split into two smaller units forward of the toilets, instead of the transverse rear galley on the later Britannia 737s. The earlier variant was a bloody nightmare on which to work, as pretty much any and all activity in the galley stopped every time someone wanted to enter or exit the toilets.
The transverse galley with the toilets placed behind the rear row of seats was a whole lot easier.
If I remember rightly, the Britannia aircraft up to G-AXNC had the split rear galley / toilets in the tail (G-AZNZ was an ex-United aircraft) and from G-BADP onwards, which were the first of the 737-204ADVs, the aircraft had the transverse galley with a lot more stowage space and working space. Of those aircraft, I think G-AVRN kept going for by far the longest of any, but mostly confined to Britannia's LTN-Belfast International scheduled services and the trooping flights in its latter days.