If the motor is vertical it would just be a case of how to mount it to the top of the truck like the current round motor. I wouldn't have thought it would need a complete re-design apart from possibly a new mounting plate.
I believe the changeover to a vertical design for GP7's was done with the C&O bell ringer, although the truck used appeared to be similar to the new PA type truck, also vertical drive. The horizontal can motor truck was based on the original Gilbert truck design. The new sideframes require a shorter truck.
Rich