That caseback would still be wrong for an old navitimer as it should be an A1 caseback but they are not repped so close is good enough.
When I made my franken Navi I used the older Fighters rep with 28k movement and the swiss 7750 fitted perfectly.
The gen dial however is too large for the case and needs to be shaved down just a tad to fit...Not a big deal.
Make sure you also track down a gen or Lello datewheel and double AR coat the crystal as these two mods make a huge difference.
Good luck;