car out of oil and seized the motor up?

Hello,

When an engine seizes up due to no oil, it can do catastrophic damage.
To find out what components are damaged, it will require disassembly of the engine and detect the damaged component and replace and rebuild components.
The complexity of this will depend on the extent of the damage. Which cannot be determined without disassembling the engine.

As for the replacement, you will need to find another 3.1L engine out of similar year grand prix. You might be able to use 3.1L engine out of a Chevy Lumina or Monte Carlo as well.

Here is a helpful video on engine replacement:

https://youtu.be/zy1CozLgWUQ

I have attached the engine replacement procedure below for your reference.

Please let me know if you have any questions.
Thank you.