what real benefit would he see going SD? just more accurate fueling/spark control?
In this case the primary benefit imo would be the reduced amount of time tuning the ecm. There is potential for performance benefits as well. With the Sunbird code you can reduce spark timing as pressure and temperature increase, there's potential to reduce boost if excessive knock is detected, and you can run low and high octane spark tables. Some of this can be accomplished through the V8 Camaro and Corvette MAF systems but you're forced to do more work before you even start the engine because you have to change the calibration so it will work with a four cylinder engine.

What's the expect horsepower level of this project?