Can you bolt a supercharger straight on to a Buick 3800 V6 without any mods?

The only mod you need is the rest of the Buick 3800 V6 engine that sits under the Supercharger!

The two engines are completely different right down to the pistons and compression ratios.

I've seen the Supercharged and the Normally Aspirated engines sitting side by side on the workshop floor and they are physically different to look at even disregarding the blower.

Internally they are different also because the engine with the blower needs stronger components to handle the more volatile acceleration.

Once you start forcing air into cylinders under pressure you are exerting far more stress on the internal components of the engine compared to an engine that is Normally Aspirated.

maybe an intake for a supercharged engine and a computer reflash for supercharged settings

All you need is a timed bomb.