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A 180B sedan almost bolts in and gives 55ltrs storage, 10 up on a 1600.
You need to lightly trim the flared sides of the 180B tank where the top and
bottom sections of the tank join, to fit it between the towers. Be careful
not to cut inside the weld when trimming. For safety, dont use a grinder,
use a hacksaw or snips. As the 180 tank is deeper, you also need to
fabricate two small (25mm) blocks to mount the tank on and bolt through
these to the original mounts. The 180B fuel gauge sender plugs into the
1600 wiring loom and works correctly. The 180 fuel filler neck fits, and
will probably be in better condition than the 1600 one.
A 200B tank is built differently. The join between the top and bottom
halves is not horizontal. This makes mounting a bit more difficult, and
the filler neck is too high to fill from the original filling position. For
the extra 5 litres over a 180B tank its not worth the hassle, in my opinion.