This is exactly the type of problem that fires me up to grind out a solution. Sometimes it ends in pain and no solution, other times you go through the weeds, a few google searches, debugging and find an answer!
So a couple of things:
I used the C3 SDK to get the project file URL in preview mode (e.g. the blob based name), since this blob URL no longer has the *.glb file extension, I changed babylon.js to default to .glb instead of .babylon. So, for this to work in preview, you need to use .glb files for your models.
The C3 project file URL SDK also works for web (and mobile), so on export, it also works to get files 'locally' (and is actually easier since the file extension is preserved on the web export.)
I moved the Babylon scripts to be local (because I had to modify one of them.)
Good luck with your 3D animations and C3, I hope to see an example of them integrated with C3 someday.