Ok, nobody helping..
So I decided to try!
Just finished assembling the transmission, and the pinion gear is fitting perfectly!
Actually it is not exactly the same.. although the number of teeth is the same, the Associated pinion is slightly bigger than the Durango, so it requires different shimming.
Durango pinion on Durango diff: 2 shims per side of the diff.
Associated pinion on Durango diff: 4 shims opposite to the gear diff.
It feels perfectly smooth yet not loose.
Track test on Friday..