Sort of same thing but i used to have an RB20 cefiro and converted it to RB25 including g/box when mine went bang!!
All i can say is that it was well worth it!!! I sourced a 20,000km RB25DET out of a Stagea so same as R34GTT one, w/gearbox + ecu, loom, all bits n pieces for just under 3.5K including shipping. That was about 4 years ago so should be cheaper these days.
The performance gain is just so so worth it. The torque, delivery, response of the RB25 is so much better IMO.
AS for what is required to do the conversion... well not sure if it is the same between Cefiro and R32, but it was crossmembers and engine mount locations, gearbox mounts and exhaust location..... then ur usual re-wiring for the loom..... fair bit of work but just time intensive....... If your budget can stretch to about $4K then do the RB25 conversion....
My 2 C
Ando