rb25 box with ppg internals. The rb26 box has the front shafts on it, can be made to run in rwd only, ie take out shafts, cut box, weld cover plates etc.. best option is the rb25 with ppg straight cut dogbox gearset, Less than all the other boxes quoted. Too make that sort of power out of the 30/26, you would need a massive turbo.. whats the car going to be used for? The skyline guys use the rb30 block to gain extra low end torque, and more air flow volume for a massive turbo.. 1500hp wouldnt be very street friendly, lag lag lag lag.. boost.. change gear.. lag.. lag.. lag.. lag.. boost.. change gear.. and so on..
Even at the power figure of 700hp, you would need to run a decent sized turbo to make that power, an extra half litre of chamber volume doesn't give you an instant jump of hp.
The rb25 will bolt on, and with ppg straight cut dog box internals will handle over 1000hp, that's the path i would take.