9 Wounds, maybe with up to 6 upon resurrecting. So lets call it 15 Wounds.
2+ save, so with no AP, 90 wounds needed.
50% of hits wounding, so 180 Hits needed.
2/3 of shoots Hitting, so 270 shots needed.
Thats 22.5 Splinter Cannons at half range, so 11.25 Venoms.
Or 11.25 Units of 10 Kabalites at half range with nine Splinter Rifles and one Splinter Cannon.
And thats not counting a good hit from a few Dark Lances or similar.
If we take it as Dark Lances, that 15 wounds needed, but his save only stops 1/6 successful wounds.
18 successful wounds needed.
You're wounding on a 3+, so 2/3 of shots, so 27 Hits needed.
Which means 40.5 shots.
Granted thats harder, needing 13.5 Ravagers, or turns with a Ravager shooting.
Assuming a cynical 1 damage per shot.
To be more sensible, lets you your list.
In your army, I see 6 Dark lances, 4 Blasters, 1 Reaper, 11 Splinter Rifles, 4 Splinter Cannons.
Lances and Blasters statistically have 10 shots, get 6.66 hits, 4.44 wounds, an average of 3 damage per shot, 13.33 damage going through.
Splinter at half range have 46 shots, 30.66 hits, 15.33 wounds, 2.55 damage goes through.
The Reaper on Beam gets an aevrage of 3 shots, 2 hits, 1.33 wounds, 1.11 going through, an average of 3.33 damage per shot.
So STATISTICALLY, you can do 19.21 wounds to Guilliamn per round.
Obviously, he only has 9 wounds, and coming back will happen between your turns. But you can EASILY take him down with JUST your firepower, AND still be able to finish him the following turn if he returns at full strength.
IF he's out in the open, and not is the closest enemy unit to all of your firepower of course.