New interview with Christopher Tolkien

[Galin]

The Appendices also note...

The 'outer' or Mannish names of the Dwarves have been given Northern forms, but the letter-values are those described.

And 'those described' would appear to point back to what was said about F, indicating a final -v sound in Gandalf as in Old Norse (if one assumes the name Gandalf is to be included here anyway).

Yet...

The still more northerly language of Dale is in this book seen only in the names of the Dwarves that came from that region and so used the language of the Men there, taking their 'outer' names in that tongue.

Here 'only' is interesting. While Gandalf as representing a Westronized form makes some sense to me, in my opinion technically the account in Unfinished Tales refers to the name as representing Westron, attributed to the North 'in general'.

Still leaving Gandalf with a final -f sound.