Pole 8, vertically magnetized blocks with +By.
Translate the upper block toward +x by 1 mm.
Translate the lower block toward +x by 1 mm.
This doesn't change the gap, so the x-trajectory is not affected much, if any.

The upper block has negative charges near the gap.
The translation is equivalent to adding negative charges at +x
  and positive charges at -x.
This makes +Bx.

The lower block has plus charges near the gap.
The translation is equivalent to adding positive charges at +x
  and negative charges at -x.
This makes -Bx.

The combination makes a quadrupole with +By at +x and -By at -x.

I1y at x = 0:  -3.6741e-006 Tm
I1y at x = 1mm:  3.9095e-006 Tm

Sensitivity:
the translation by 1mm in both the upper and lower blocks changes I1y by 7.58e-6 Tm as x changes by 1 mm