Your driveshaft should be the same length but you will need to have a new flange put on to adapt to the R200 diff. (Z31 and S12 Had different flange types)
I used a Diff and axles from a Z31 300zx turbo so the axles were a little different than the Turbo and SE model S12 axles.
(I converted to Z31 rear 5 lug vented rotors. Hints to why I needed Z31 R200 axles, stub, etc.)
But the basics for the swap as stated above R200 diff, R200 Axles to match the Diff and stubs, R200 Diff mount off a Turbo or SE model S12.
My Rear end set up is as fallows.
Z31 Rear control arms with vented rotors all new bearings
Z31 R200 Diff with Finned diff cover
KaaZ R200 1.5 way LSD
Z31 R200 axles (Note: one of the Z31 axle stubs is longer than the other so it matters were it goes)
Se R200 Diff mount (I ended up filling up my diff mount with poly urethane to stiffen it up some)