Yes, you are correct, In fact the 87-88 z31t trannies are identical to the RB25 tranny with the exception of the bell bolt pattern. I see no reason you couldnt use a 87-88 tranny for this. I dont think it will make a tranny mount any easier, but if all you're concerned about is the shifter location then there ya go. the 87-88 trannies are just typically harder to find . . .
I'll drop a hint though . . . Im not 100% positive but I think that the Later VG30e 2wd pathfinders may have used this "shorter" transmission. Someone needs to check it out. In a similar way, the nissan trucks, hardbody's,etc. used a shorter version of the "C box" tranny aka 240sx tranny. The "stubby C box" if you will . . .
Isnt Ricks Pathy a 2wd? roll up under there and check it out. . .