It isn't clear from your description what alloys they are (as you acknowledged, the badging -- viz. GL, etc. -- doesn't indicate that it should have any), so it's likely the previous owner got them on his own.

Anyway, re your comment, "If the handling isn't what I had on my other 240s I'll switch to steelies, too.", alloys (if they aren't defective) almost always improve handling.
One reason is their lighter weight -- this lessens unsprung weight (the mass that isn't supported by the springs) which in turn allows lessens the inertia or momentum of wheels/tires, and this allows them respond (change directions, accelerate) and follow road irregularities.

Another reason, for some alloys, is that those in a wider size improves the tires' response to steering input and resist cornering forces. The standard (steel) wheel is 5.5x14. If your alloys happen to be wider (may or may not, depending on the wheel), that tends to spread the sidewalls and (up to a point) helps them generate greater side-forces (for cornering); the sidewalls are also made a bit more rigid, and therefore the tire will respond more quickly and precisely to steering input. Obviously, an additional advantage of wider wheels is that you can fit wider tires the next time you need to buy them.