That's NOT a conversion or roof raise which is so popular today. It was built that way by Crown for a US Post Office contract where they were driven on overnight routes with folks inside sorting and getting the bags ready for delivery to outlying PO's or collection centers, usually between city centers connected by highways. duuhh. Pretty innovative actually and it was a obviously used on routes not well served by rail, or air, or other time/distance
calculations. Filled a need and eventually became obsolete as things changed, and we don't see new built ones today on the roads.
That's why they are always referred to as Highway Post Office Crowns, sometimes Hi-Po's but whatever you call them we all know what they are. They were all standard horizontal mid-ship mounted engine configurations with standard Crown everything below the raised floor and roof. Like I've always said Crown was first and foremost a CUSTOM Coach and Body builder and whatever the customer wanted Crown would and did engineer and build from the ground up. A Lost art and sadly probably never to be repeated in today's mass produced chin made throw-away 5-10 year life-cyle era.
The one thing against them is the age thing, most were built in the 1950's and had either Hall-Scott gas guzzlers or early Cummins 220 non-turbo'd maybe re-powered or possibly built new with the diesel. They are truly old and a vintage Crown with all sorts of challenges. Plus I think they had lots and lots of miles put on them so that's to be considered. Crowns can do 1M miles easily but not without good maintenance and keeping up on parts replacement.
These old Crowns have systems in them that are very hard to find parts for today and would best be updated to ease upkeep. The body is also the one thing that can't be replaced so long term exposure to rust and corrosion is to be looked at and considered. The ones I've seen were all in need of lots of remedial repair and not something I was prepared to take on. But that's just me. I drove plenty of 1950's era Crowns with gas and diesel engines back when I wore a younger man's clothes but I wouldn't get one for myself with all the newer ones around and about, which is exactly what I've done. Less headaches, which is all a relative term, and easier to get parts today. I'd say any Hi-Po Crown must be considered a real project bus and approached as a money sink, a DEEP money sink.