GO FOR IT!!
I used a Calmi donor. It was too difficult to find a Japanesse donor. For the front diff, I swapped out the WHOLE diff, just had to put on the stock Vit/Track brackets to hold the front of the diff. Way easier, no real reason to swap the pot's.
I could not find out the reason for not using the Calmi diffs. The write up refers to swapping out the Side/Track third member into the Vit/Track pot, which may have been the original problem. Since I kept the unit as a whole, its been fine.
Otherwise, stock hubs are great. Try to get a second set in case there's a seized one.
Since your down there you should beef up the cross member mount. In the link below at the end you can see how a steel strap is bent over the rear of the front diff, definetly needed if you have an aluminium housing.
http://www.zukiworld.com/month_020103/feature_frontendupgradeswithhagen.htmIf you have the steel housing. I would STONGLY suggest that you don't worry about the Calmi issue, pull the ring and pinion and have that put into your steel third and pot.
FYI, your stock rear diff's housing (can) for the spider gears should be the same as a sammie's (easy way to check, is to call about ordering a ratcheting locker). Keep this housing/can, as it is needed if you ever want to put a ratchetting locker in the front. Refer to the link to check what I mean.
Mine has been great for over 2 years. Presently I've just busted the Cursed Aluminium housing that holds the pinion (search 'busted front diff' to get an idea of how weak it is). I must now get a new front diff and try to find a steel Vitatra diff to put the Ring and Pinion In (and locker
).