I just ordered the above from AH Spares and the box came today, consisting of:
AH Spares Part number/ Part
RAX124HW NTN, Japan. Label on box was obscured, but bearing itself had a 4T002420 on one-side and 4T-02474 on the other (I
think - my eyes and the clarity of the stamping are both deficient)
RAX126HQ consisting of two Timken boxes (labelled don't open until assembly), with one labelled 3420, and the other 3478

I'm going to let the differential guys worry about the number of boxes etc., but will report in when I learn more. Hopefully this will take care of the unhappy whine out of my shiny new 3.54 diff set (it was in and out of the shop and the car a couple of times last Spring; touch wood, it'll go in once-only sometime this forthcoming Spring!)
I perhaps could have tried researching the subject more prior to ordering from England, but I trust that the guys know what they're doing - but figured I'd share in case others can source the bearings more locally (and not have to pay the courier service their pound of flesh).
Later, Doug