As Terry said 315 Sqn did not strip their Mustang III's until after the war. But 65, 19 and possibly 234 Sqn flew their Mustang IV Silver Birds over Norway in the last months of the war.
If you get Halvor Sperbund's "Brennpunkt Westküste" there are a couple of 19 sqn QV-marked Mustang IV's. The book comes highly recommended. And if you don't want to get the book just contact me by PM or offline
Kyrre