Manny, I am more versed in the Historic Manual winds than the Contemporary Automatics but I would expect that your dial will work with either 7750 since the gen OP movement is a 7750 base.
I would suggest going with the Cartel Ultimate 104 case and use a T-48 Crown,,,I think you are going to run into less issues than starting with a DSN case which always seem to be a crap shoot.
Since you have the Gen hands, you should be OK with a Swiss 7750 - as to which A7750 would be the best fit, I would have to defer to Ziggy.
My 090 Franken used a Gen OPIX movement (7750 base) and we used a standard Rep case with the 7750 movement spacer and all worked fine. I had to have a Gen dial though to fit properly. The A7750 Rep dial would not line up correctly...
Sounds like a great Franken in the works. Look forward to seeing the results.