First, I'd keep it as the kind of tour through several lands that it's set up to be in Ustalav, so the following would be best for parties that don't mind walking.
I'd probably start things of in "The Haunting of Harrowstone" in Mordent, having the PCs drawn to Mordentshire or other town not on the map (even Ravengro itself) in much the same way as it's set up in the Carrion Crown Player's Guide, having them be related in some way to a scholarly ally in town, whether it be Van Richten or one of his near equally learned allies. From there, it'd be an easy thing to place Harrowstone outside of the town or nearby. The adventure could proceed pretty much as normal from there.
From there, we get into "Trial of the Beast", which starts with a good long overland journey and some encounters along the way. The PCs could meet the traveling freak show while they're passing through Dementlieu then go on to Ludendorf, which would take the place of Lepidstadt. From there the adventure can progress pretty much as normal, subbing in Schloss Mordenheim for Schloss Caromarc. (Whoa, that's all fits creepily well... I SWEAR it wasn't planned like that and that this is TOTALLY the first time I'm thinking about this. *awkward chuckle* Anyway.)
After that we get into "Broken Moon" territory, but there's no way I'd have the campaign swing all the way back down to Verbrek. Rather, I think I'd use the Forest of Shadows as the Shudderwood and use Corvin or a community on Lake Placid or Redleaf Lake as the Ascanor Lodge. From there I'd swing south to use the City of the Dead as Felgrau.
Departing from there there's another good long journey to the coast with "Wake of the Watcher". The problem here is that the closet coast is way farther away in Ravenloft than it is in Ustalav. I'd probably just hunker down and use Nevuchar Springs as Thrushmoor and then put Illmarsh farther away to the south, somewhere halfway between Nevuchar Springs and the border with Nova Vaasa on the coast of the Nocturnal Sea.
With the trip to Ravenloft Illmarsh taking us halfway down the coast, the closet cosmopolitan center to sub in for Caliphas in "Ashes at Dawn" would be Egertus. That adventure could play out there with little trouble nearly unchanged if you don't mind giving the city a bit of a vampire problem. Though, since it's already set up as a serial killer murder mystery, you might be able to spin Malken in there somewhere.
For the climax with "Shadows of Gallowspire" things get a little trickier. Thinks wrap up in a cursed mountainous wasteland. If you want to play things close to the way the AP presents them heading into Barovia and Mount Sawtooth might be a good place to drop Renchurch and Gallowspire, or even on to Forlorn, or even the mountains of Hazlik since that seems like good grounds for liches. This close to Castle Ravenloft, though, it gets pretty tempting to pull Strahd into the mix, and I might start thinking about respinning the whole plot as some new gambit by Strahd to escape the Demiplane of Dread by collecting and distilling essences from points of power across the domains into an elixir that would allow him to transcend, escape, or even become one of the Dark Powers. Runchurch could be near the village of Barovia and then you could sub in Castle Ravenloft and a fight with Strahd as the big badness at the end.
Actually... that sounds pretty @#$%in' sweet!