If you have the stock motor and no complimentary upgrades to follow with the 450cc's (or 1G style injectors), then put the 390 cc's back in.
What you need to make the 450cc work properly and without much consequence is as follows:
1G 4g63t ECU (main computer behind/below the factory radio)
1G FPR (fuel pressure regulator)
1G 450cc injectors
1G MAF (mass airflow sensor)
Fuel pump rewire kit
Intercooler and piping
Boost gauge
Full width 4g61t radiator and fan(s) if you only have the half size
If you want to up the boost you can add:
MBC (manual boost controller)
1G early or later model ECU with EPROM and tuning for larger injectors and deadtimes, fuel maps for higher boost ceiling, MAS upgrades, etc)
1G cams
2G MAS
Wideband 02 sensor and gauge
This is the safest approach currently available, where no tuning is required and will be turn key and go, if all parts are working properly.
Once you get into random cams, higher boost, datalogging (well you should have this anyways), AFPR (aftermarket fuel pressure regulators) and so forth, it becomes quite complicated and less fun in my books.
Stay close to stock in terms of components and it will be easier to replace, repair and still bring lots of smiles to your face.
If you cannot afford to break it ....
Manuals here:
www.lilevo.com/mirage/
www.lilevo.com/mirage/Manuals/
Get the engine running correctly on the stock sized and matching components then move forward.