If you need to do a full drive-cycle for re-certification then it's usually best to do the minimum changes initially so you change the base car as little as possible.
Get it (re)tested with the new engine configuration and once it's approved you can then usually work within that new setup to get your desired config.
Eg. on a SC you would probably want to install all the bits, make it chargecooled if wanted, but run it with the completely standard OEM exhaust and cat (with pre-cat!) setup and use a big pulley on the SC so it makes only a tiny bit of extra power. Aim for around 200HP max.
That should have no problems to pass the drive-cycle tests including any noise tests. (likely you will be classed in a higher CO2 kg/km class though..)
After that you can of course do more 'stealth' modifications like going to a smaller pulley, better exhaust with a sport-cat, etc. so in the end you sould be able to get 260hp or so out of it and still pass regular yearly MOT tests as from the outside it all looks the same
With an ITB setup the best would be to do nothing at all to the engine itself from it standard normally aspirated form (no cam change, no head work, no pistons, etc. etc.) and only get the ITB's working and make sure all emission related bits are working well and that it's mapped properly with good closed-loop lambda control. Extra care needs to be taken on these to get the noise down as that will likely be a part of the test, so some enclosure around the ITB's and a common air filter (perhaps even re-use the normal filter and housing).
It should really not make any extra power at this point and if you have it re-certified with ITB's it should also get pretty much the same CO2 kg/km rate as the engine is still the same 147hp N/A, just on throttle bodies. Properly mapped for good cold start and warming up strategy it should be able to reach similar emission levels.
Once that's done then you can open up the engine and start bumping compression, cams, valves, etc, etc, etc...
The SC will likely be the least difficult path to take as that keeps virtually all OEM parts including the (re-programmed) OEM ECU with all it's emission strategies and the SC itself is an OEM GM part too.