You can see what it is supposed to look like here
HOW TO: P11/B15 transmission swap into a B13/B14/P10 - SR20 Forum
The transmission in that write up is a RS5F70V. I don't know if the Primera also got the LSD transmission. What really gives it away is the black cover that is on the front of the transmission. You can see it in the pictures. That's how you know you have the stronger transmission. Over here in the states the 99 P11's received a weaker RS5F32V.
The non lsd version of the stronger box is a RS5F70A. You can tell between lsd and non lsd by the hump on the left side axle. Also the LSD transmission has different diameter oil seals. There is a Nismo LSD available for the NON lsd box, part# 38420-RS360. They are still available but you would probably have to source it from Japan or maybe Australia.
In order to use the non-lsd unit you would have to source a non lsd left side axle if your car is originally equipped with an lsd transmission.