The RD28 is a very different engine and not going to be any good for you job.
RB30 is not anything like a bolt in to a GTR and the cradle etc needed to fit the sump is very expencive and not as good as fresh Tomei parts.
They are all made in china and if you buy the good ones then their as good as any jap manifold and cost well under $1000 in Australia.PER4MANZ(0893586383) has them now and we have a heap coming.
Aftermarket ECUs all effect autos but we have had no real problems.
Sensor benders also effect autos if you need to make large changes as the load values etc are substantially altered and do alter the Autos performance.
Worst case we have had is like a mild shift kits been fitted.
25 Box fits but the shaft does need to be changed and a few other small easy changes.
25 head share bore and bolt centers but every thing else is wrong like water gallerys etc.
Wish you ran last nite Sean,Lots of PBs as the track was on song , time to enter super street to get a run on a proper prepped track.
This beast has much more power in it just Sean keeps the tune soft to look after the stock motor.