by looking at mazdatrix picture, u can simply assume that
S4 after VIN 608385 and ALL S5 TII halfshafts are longer :
Get these S5 TII longer halfshafts and then shorter S4 TII stub shafts (S4 after VIN 608385, part number shown in picture.
That should be ok.
We run FD torsen in about 10 FC's so far, its most affordable LSD for us...
Swap is pretty straightforward, set backslash and DONT forget to glue bolts to the ring gear (on one of our diffs they did break loose and it did not ended up good
)
Here are some pics from swap :
http://rx7cz.net/photos/workshop56/