What must be done to swap a 1989 3800 engine into a 1997 Cutlass that had a 3100 engine?
The '89 engine and trans came out of a Reatta.
It sounds like your taking on a big task.
The issues involved will be engine mounts, computer connections, computer programming, wiring modification, exhaust and the list goes on.
If you are a mechanic with the skills and knowledge to handle this kind of swap then it can be done. If not then do yourself a favor and find the engine that belongs in it so you can have a trouble free swap.