The type was used on Midways and some other ships - no idea if the specific guns had been made - but if they were then they would have been used on something.
Nothing specific was made and they didn’t started hull construction. With current ruleset it won’t be added, since it wasn’t laid down.
For Soyuz, for example, you can quickly find pictures from the shipyard showing the laid down hull under construction. As well as a concrete test mount for the main gun barrels. Similar for the german H-class.
But I could totally imagine Gajin goes WoW’s way and just starts adding total paper projects. So its not impossible to get Montana in future. I personally won’t like it, since these paper ships seem to always overshadow real existing units by a large margin and make them pointless to play. Thats the huge downside with dream-like projects which never suffered reality checks and practical restrictions.