It depends... Does your car have ABS/HICAS? does the donor car?
http://www.texasnissans.com/tx/forums/s ... hp?t=12855
^there's a great source of info for the vlsd swap for an S-chassis. All USDM sourced vehicles. Depending on what you get, it may be as simple as swapping your diff cover, or as complex as either replacing axle stubs and/or axles and getting a new driveshaft.
I don't generally like redirecting away from the forum but that's about the most consolidated place I've seen all of the R200 swap info.
Cliff notes (assuming a VLSD from a J30, Z32, or S14 w/ ABS
If you own an S13 (89-94) you will need to swap the rear cover off your stock open diff onto the VLSD:
The S13 uses a different bolt pattern (4 bolts) than the S14 (2 bolts) on the rear cover...
You will also need 2 longer mounting bolts for the S13 chassis, and 2 large washers for the front mounts...to be used with the large bushings on the front mounts.
They are M12 X 1.25 thread/pitch, 85mm long.
The stock S13 front mounting bolts are not long enough for the J30 and S14 diff mounts.
And I've seen more than few diffs drop out from the front mounts by not using washers - They need to be ~1.5" diameter or so, and 1/8" thick.
To overcome the .75" extra length at the nose of the diff you can:
1) Install it and see if your driveshaft and tranny mounts have enough play to soak up the extra length.
2) Get a driveshaft from an ABS equipped 240SX...it's .75" inch shorter.
You can also swap the VLSD "guts" into your stock open diff housing:
If you buy a J30 diff but would like to keep the stock 4.083:1 ratio...open it up, remove the VLSD center section, and swap it onto your open diff ring gear.
Sounds easy, but it's a time consuming process, and if you mess it up (have too much or too little clearance or backlash) - You'll ruin the gearset.
I've done it twice succesfully, so it's not that hard or scary...but you need to take your time and put EVERYTHING back EXACTLY where it came from (shims, bearings, etc...).
And to make it VERY clear...you use the VLSD center section AND output shafts...with your stock open diff ring and pinion / case / bearings.
You don’t have to use a fluid designed for an LSD as the R200V uses a sealed unit.
Nissan recommends 80W-90 oil, 1.5 liters (3 1/8 pints)...
Do you already have a 180sx diff or something?