It's a 6 cyl, but supercharged will be an issue for power restrictions even though you can buy a factory 6 cyl with more horsepower than that thing - their supercharged 6s weren't exactly high horse power (though I suspect you could do a lot more).
Anything that looks worked on is always a risk - if it's being sold, then chances are that it's been given a hiding already, and it's probably due for a whole lot of work that won't be cheap. Anything that's pretty much factory might be a little more boring, but better chance that it's been taken care of, and probably good for a lot more miles. And they don't attract unwanted attention.
If it was their pride and joy that they took good care of and never thrashed it and they just made it for show, and so and so forth, then they'd need a real convincing story as to why they're selling it... and chances are they'd be asking for a lot of money.
But.. I'd always be wary of cars that look good. The types of drivers who do that to a commodore are the types of drivers that they usually have a field day with when they decide to give you a random breath test, drug test, and while they're at it decide that they have grounds to search the car and go over it for defects. And shit, at this point you probably haven't done anything wrong yet.