You might want a regular mechanic to check it out. IF the crank broke or you have serious internal issues, being a Comp G all you would need is a good low miles shortblock, THIS is all the bottom end parts, then have heads,intake, blower etc swapped on and either find local tuner or as its being repaired or doing the repairs your self get a "topswap" tune. The more expensive route is locating a new/used supercharged engine complete. The reason for computer needing a "topswap" tune is that non supercharged bottom ends or shortblocks have higher compression and it can "knock" or KR its self to death if you beat on it or get bad (low octane)gas even. The shortblock will basically be everything below the heads/intake. Most people with NA cars are doing "topswaps". I have an 04 I picked up with rod knock, still trying to figure out getting it home, then I need new engine/rebuild and see how it drives. Hoping I can have it ready for winter! Mainly cause car I have now has no heater! and I am putting off pulling dash(I am a tech by trade so as they say mechanics car gets worked on last) to replace and car needs so much more work. My mom gave it to me and hope to be able to drop driving it and start repairing it.
Oh well back to your issues, Get it properly diagnosed. Then make plans/decide on course of action. AND WATCH OUT ,DONT LET MECHANIC TELL YOU IT ISNT WORTH FIXING WITH OUT DOING RESEARCH. Because unless the car is rusted out underneath or has major damage somewhere N/A engines can be found for very little cash. Heck you can get N/A complete engines off ebay for $300-$400 shipped just watch ads cause some are super high miles engines.
OH and any 3800 Series 2 or 3 shortblock will work. up to the year GM discontinued them. The only changes were minor. And 3800s from Bonnevilles, Lucernes, etc all work you may just need to swap oil pan/pickup. and of course your top end id its N/A engine.
OH and IF your engine broke and a piston hit a head get the valve checked before bolting it on different shortblock.
OH yeah, 2004 and up with throttle by wire are using GEN V superchargers so if you picked up older L67 supercharged engine you still need to swap on your lower intake, and supercharger but wont need "topswap tune" as all S/C cars have lower compression engine from factory, makes up for blower.