I believe at least one of these used to run as a bus between Portland Oregon and Seattle Washington. I saw it for sale about two decades ago, luckily restored, but I have no idea where it ended up. It's certainly not in any of the local auto museums.

I wish I'd had one of those when all of my kids were home!

In reply to "Perhaps a Real Station Wagon", no, the term "service car" is perhaps unique to New Zealand, where it meant a long haul passenger vehicle that was operated between main centres, much as buses do today. The term predates this Cadillac by at least 30 years.

Extended muti-passenger automobiles were in common usage to
pick up hotel/resort guests at the train station and drive them to their
destination.