[CNHSS1]

mk2 s12 and s13 are identical box ratios (in the uk anyway). S14 box can be used to replace any car using an s13 box if the S13 CA style belhousing is used rather than the s14 SR type. Straight swap, 20 mins for the bell housings.
As Martin said, s13/14 ratios are on the downloads, but essentially the s14 box gives longer 1st and 2nd, almost the same 3rd, identical 4th (1:1) and slightly shorter 5th. Its essemtially a 'close' ratio version of the S12 mk2/s13 boxes. There are afew variants of each of the boxes. I have had 2 different s12 mk2 boxes, 3 different s13 boxes and 2 different s14 boxes, but they are detail changes and only some parts are interchangable.
Ultimate box design is the last s14 boxes which have a 'trapdoor' design (similar to winged anti surge engine sump pans) on the centre steel bearing carrier that stops oil starvation to the bearings and gears on hard accelertaion and G loads.