Hmmm, guessing you're not the best of friends huh?
I don't know much about the model, but you're allowed to run whatever driveline the vehicle series came with. ie, if an RB25DET was available, you'd enter it as a Cefiro RB25DET. If the largets engine was an RB20DET... then that's the best you can run.
For istance, my r32 GTS-t has the RB20DET, but if I were to enter the vehicle as an R32GTS25, then I would be able to run the RB25DE, but NOT the turbo DET version.
That's my understanding of the rules for this era of vehicle.
Now, earlier vehicle I believe can have much looser regulations if they run in "modified", ie, Toranas with 7L Chevs. 5 link rear ends etc etc... but not this era.
Hopefully Stewed Balls will pop on and answer this much neater....