What I had planned on doing was stripping down the custom OS's, so for the NOS guys, they simply have the monitored input and the fuel / spark tables to match, that was it, no TPS VE, no Boost VE etc.
Doing it this way means the possibility of adding a NOS custom OS to all 55 GenIII operating systems makes it a less daunting task and also gets the job done quicker.
PCM Flash memory space constraints will dictate that a custom OS5 cannot be done on many 2004+ OS's anyway.
Of interest, I mentioned above 55 OS's for the GenIII, this is since 1998, for the GenIV, between just the E38 & E67 there is over 50 OS's we support for them since they came out in 2006, this is where much of our R&D time is going at the moment. What is GM doing!!!
Have a think about how a simplifed NOS custom OS would work for you.
Cheers,
Ross