The W-series are just the driver, no enclosures...
The T-series have the enclosures.
The 0, 1 or 2 are the size of the drivers.
The bottom picture are the mock ups of the enclosures to see what would fit where; with the 1925S used in hood units and the 1931S in cab, possibly.
The BIG one, the 1828S, might shoe horn into a large tender. wink... ;<