A series 3 R31 runs a box pretty much identical as the R32 RB20det box except for the second gear synchro(single VS dual???). Series 1 and 2 R31 box's are different too series 3. A GTS2 is a series 3 R31, so following that logic, the box would be almost identical to an R32 RB20DET box.
Suspension wise they had a floating front hub arrangement with larger calipers, and 100mm bolt spacing instead of 90mm, these GTS/HR31 struts are desirable for brake upgrades, or for datsun coilover conversions. Some GTS's had a factory camber/castor adjustable strut top. The rear brakes were as per standard IIRC. They had factory bilsteins, better seats/interior, factory bodykit, ECU chip/remap, stainless steel exhaust and possibly a different cam. GTS1's are all white, GTS2 are all RED.
That is all from memory, go to www.r31skylineclub.com for more info. http://wiki.r31skylineclub.com/index.php?title=R31#GTS2 no mention of a different box