The GB7 Xtender is a direct fit for most Warwick basses. However, in most cases the Xtender will not drop down a whole step. This is because the Xtender lever comes into contact with the adjacent tuning machine, preventing the unit from rotating fully.
One possible solution is to remount the Xtender and other tuning machines so that the pegs sit perpendicular to the bass' center-line. This requires drilling a new mount holes.