Does anyone out there know for sure if the front 3rd members on stock 1986-1995 Samurais are the same ratio? I know the fronts are not the same as the rears but are all fronts made the same? 
Reason for asking:  I want to put an early year front 4wd axle under a later model 2wd Sammie.

All OEM US Samurai (SJ-413) differentials (both front and rear) have the same gear ratio - 3.73. 

Unlike the Tracker/Sidekick differentials, the Samurai front/rear differential housings and ring & pinion sets are completely interchangable.  The Sidekick/Tracker FRONT differential is - with the possible exception of it's sidegears - can be installed complete on a Samurai although this is inadvisable as the case is aluminum and not steel. 

The Tracker/Sidekick rear differential is physically larger than it's correponding Tracker/Sidekick front differential even though it has the same ratio.  It cannot be swapped into a Samurai unless you replace the entire axle - housing and all.

The only thing that is different in the differentials thoughout the Samurai production years are the axle spline counts of the sidegears from the front axle to the rear axle. BTW, sidegears have no effect on a differentials' operating gear ratio - only the ring and pinion gears do that...

I don't offhand know which years the change occurred in or the exact spline count.  Perhaps someone else can post that info...

I hope this helps!

All 86-95 samurais have 3.727 (3.73) gears.
All have 26 spline rear sidegears.
All have 22 spline front sidegears.
All rear carriers are 4 pin.
86-88 front carriers are 4 pin.
88.5-95 front carriers are 2 pin.
I do know the 2 pin carriers are made differently than the 4 pin carriers (but they will still interchange between thirds).  The 2 pin carriers look just like the trackick front carriers (they may be exactly the same, but I don't know for sure though).
IIRC, to put 2 pin carrier sidegears in a 4 pin carrier, the sides of the sidegears have to be ground off just a little bit (the sidegears have a "ridge" around the outer edge).

To the OP......short answer......any year samurai front axle assembly will work fine in your 2wd samurai.

Thank you so much...VERY informative....Holler at suzukijohn.com if I can ever help you with parts, etc...

1985 SJ413's have 393 or 390's and will bolt into 86 and up. They are rare, only one year done.