Well I've done some digging and the 4-stud shaft is a "Double Offset Birfield" type" and the 6-stud is the "Tripod-Tripod" type. Other than the name I have no informatin on one or the other. However, the companion flange in the suspension arm looks to be specific to the driveshaft and the part is listed in the various US nissan parts websites. Looks like the s12 was only ever the T-T type.
