now that is one find ;)
Looks kind of too well done for a mule, but then again, who knows. Could be a skunk works special for the Sultan of Brunei (he has a lot of special Mercedes') or comparable "not exactly living on social welfare person".
If a mule, my guess is SL, it is the oldest Merc (apart from the G-Class, which is "slightly" older then the rest of, well, nearly everything human kind knows)and not selling, proportions/size would fit. Aston mules used to have Aston bodies, even teh Merc related DB1, so I don't think it's that.
Probably Mercedes is even reviving the SLC (the 2+2 fixed hard top SL form the 70ies), in which case I'd also love to see the return of the chromed side louvres ;)