If the stock engine is healthy, it can make some very fun power, but will need a list of work to do so reliably.
These cars are pushing 38+ years old and with them being EFI any little issues in the wiring, grounds, vacuum lines, exhaust leaks, fuel system ect.... can cause a ton of headache and other costly problems.
Read though this website, its full of great info and is a must for a car that has not been driven for a long time.
The low hanging fruit is:
-Full tune up (google search "Spring Cleaning Turbo Buick") or go to
The Grand National / T-Type / Turbo Regal Buick Spring Cleaning Guide
-Fuel system. this must be 100% solid, no questions or shortcuts. Plenty of info out there, you just need to research and learn.
-Replace the stock nylon coated timing set if it still original.
-Valve springs, the stock units get weak and can decrease performance significantly.
-Vacuum and exhaust leaks need to be addressed. These are both common issues.
-Modern ECU Chip specifically for your car and your goals. (turbotweak.com)
-Gauges and devices to monitor the ECU such as a Scan Master and ideally a Powerlogger.
As far as power, the above items MUST be addressed first. The stock turbo can make a decent amount of power, but no turbo upgrades until the items listed above are addressed. Octane will be one of the limiting factors on how much power you make with any given combination. The use of Alky Injection or switching to E85 is the most common approach for a street driven car to increase octane which in turn allows for more boost.
Best of luck. The search feature is your friend. Tons of info on this site too.