Friend of UWVisions Jacques-Yves Phelipot has posted some photos on French forum, Le petit forum de la Photosub about the process of fitting an F.I.T. adapter for the INON 45 degree viewfinder to a Nauticam housing. Adapters are available for all Nauticam housings. The tool you see in photo 4 is the Anthis viewfinder removal tool.
Thanks Jacques-Yves for taking the time to post:
UnderWaterVisions's News 
I try to mount, i attach before inon to adapter, ther toghetrer to the house, but the “stop” wasn’t in the righ position… what i must do?
Where did you get the adapter from?