you could possibly fit the 3.54 ring and pinion into the old 4.7 Series diff housing which has the required 10 spline centre, this will remove any bearing incompatability apart from possibly the one on the pinion shaft
so you'd have to remove the inner race from both shafts and swap them over (a pig of a job)
next problem will be the pinion height which is set using shims and a dial guage by rights
and finally there'll be the need to centre the ring (crownwheel) correctly to the pinion to get it meshing correctly
it's been a long time since i looked but google "Crown Differentials" as he had detailed write ups from memory on the differences between early and late diffs and how to assemble them plus can sell you the required shims and bearing adaptors if needed
Kam Differentials are also a useful source of parts
i have personally mixed and matched early imperial 4.3 (yes 4.3) parts into a late metric 10 spline 3.54 housing and centre due to the bearings having collapsed in the original 4.3 housing, half the bearing measurements between metric and imperial don't match but the really lucky bit was the pinion shafts were the same diameter
my build wasn't done to the manual but by feel, i got away with it and built a nice quiet diff but you may not
hope that helps
, it was just another idea for him to work with which is why i also suggested he looked at Crown Differentials for the details 
