Some additional pictures for the discussion:
Back side of a 1947 gauge set up against a later post 48 version.
https://www.flickr.com/photos/advance-design_parts_co/13748476365/
https://www.flickr.com/photos/advance-design_parts_co/13748869604/
Notice the difference in the tabs, and the wiring harness attachment, the mounting to the dash is significantly different.
Picture of 1947 speedo/gauge backs.
https://www.flickr.com/photos/advance-design_parts_co/13748868174/
Also pictured is the block off plate that covers the mast hole where the column enters.
https://www.flickr.com/photos/advance-design_parts_co/13748509423/