The main differences between the 130bhp (96kW) and 150bhp (110kW) SR20 engines are the intake cam, exhaust manifold, exhaust, and ECU mappings.
I've just sold Neil (Neil82 on this forum) the intake cam and exhaust manifold from a 110kW 1998 Primera GT, so speak to him in a month or so and I'll sure he'll let you know what difference those two mods gave him.
The 1999 Primera does indeed use roller rocker cams, and therefore JWT do not currently have any cams that will work on your car. They are in development I believe, but I have no idea as to a release date...