[RarlyL8]

I think a direct answer to your question is "no" you cannot make a Carrera engine out of a 930 engine by simply removing the turbo.
The 930 is a true turbo engine, meaning an engine built specifically to be turbocharged. A Carrera engine is EFI with ~10:1 compression while a 930 is CIS with ~7:1 compression.
The 930 transmission is also built specifically to be used with the long legs of a turbocharged engine and would be a miserable experience bolted to a Carrera engine.
The turbocharger is an integral part of a 930 engine and the specific component that creates the power. To remove the turbo from a 930 engine or add a 930 4spd to a Carrera engine would be akin to hobbling a race horse. To do both would be worse than driving a 912 sportomatic.