Hi xnke
i think reversion wont be a problem with that length inlet ,, the cam plays such a big part as does the exhaust manifold , last year i engine dyno a engine that was spraying fuel 3 feet out from the carbs and we changed the exhaust runner length 2in and it stoped , its not in the inlet port from all the testing we did last year , all my heads have 39mm + ports and never have steps in them , things to note short runner manifolds with 300d+ cams and long primry pips will have reversion , you need at least 13in from valve to trumpet ,
as for the gtr even stock engines that make 280hp are very hard to tune with some ecu , the map signal is so week and the tps can be is 5 places with boost and vacuum , at part throttle there a real thing to tune ,