. . . but here are some clues to look for in determining what it is:
1) a 380SL is 107.044, but the 560SL is a 107.048 (I'd think one or the other number should be on an underhood or door jamb plate)
2) 380SL cam covers are silver/aluminum color with raised longitudinal lines, 560SL cam covers have the same lines, but are black
3) a 380SL's air cleaner snorkel ends about even with the front edge of the cam cover, but a 560SL's air cleaner snorkel goes all the way to the radiator support (it has a rectangular funnel that bolts over a hole in the support for fresh air)
4) a 380SL's distributor is 3-4" in diameter; a 560SL's distributor is more like 6" across.

I imagine one of these is true:
- the PO only changed the 380SL badge to a 560SL badge, or
- the PO also swapped engines (in which case cam covers would black, whether he put in a 560SL engine or the more powerful one from a 560SEL).
- the PO not only changed the badge and engine, but also perhaps the air cleaner and/or ID plates.

Assuming the ID plates were not altered, the VIN would provide more info, but I don't know what was made within what VIN range.

I've also read that 560SL bumpers are closer to the body and perhaps have different side bumpers as a result, and there are probably differences in the interior and options, but I don't know what.

For price negotiating, point our each inconsistency to the seller as a reason to reduce the sales price from the "book value" even though you may be happy with the alterations once you buy it.

Since you're local (Seattle), drop me a private email with your phone number if you'd like me to share pictures I've collected of the differences or get together - either to play buyit/don'tbuyit (a derivative of goodcop/badcop) in your negotiation, or if you get it.