The WLC is now fired like a canon but with the following differences.
The second artillery dice not only indicates the bounce but also its strength. At the final impact, you place the 3" template. All models touched by the template, as well as all models on the line bounce - final impact are hit with the rolled strength.
No armour saves are allowed and each hit causes 6D wounds.
So it still can have a crippling effect on the Stank. But do not forget the Orb of Brass: if hit (initiative test), the Stank is gone.
To be complete: the WLC cannot fire shrapnel. If forced to flee (for whatever reason), it is automatically destroyed. Crew and canon are considered one model. Against ranged attacks (including magic) it uses the toughness of the canon (i.e. 6), in close combat the toughness of the crew (i.e. 3). The combined model has 4 W.