A preliminary investigation of how Barks may have changed the story:
Donald has three nephews, while Mickey has two nephews.
In panel 1.4, Mickey's nephews may have been drawn slightly larger to fill up
the space of a third nephew.
In panel 1.5 it's difficult to find any place, the third nephew may have melted with the bushes at the left. Maybe it was at the right of the box, if that wouldn't take the effect away of the waving bushes at the front right of the panel.
In panel 1.7, the third nephew may have been in the blank space at the right.
In panel 2.3 and 2.6, the third nephew may have been in front of Gyro's left leg.
In panel 2.7, the third nephew may have stood in the middle of the remaining two.
In panel 2.8, the third nephew may have been in front of the sign at the left.
Panel 2.3 may have contained only two nephews.
In panel 3.1, two nephews may have been replaced by the one shown as silhouette.
In panel 3.3, the nephews may have been drawn slightly larger to fill up the space of a third nephew.
In panel 4.4, the space of third nephew may have been filled up with the bushes at the right.
In panel 4.7, the nephews may have been drawn slightly larger to fill up the space of a third nephew.
In the dialogue of panel 2.8, the nephews refer to Grandma Duck by calling her "Granny Duck". In panel 3.2, Gyro calls her "Grandma", but the lettering seems to be a bit different. Maybe he originally called her "Mrs. Duck"? If so, then this change may have been made to Gyro and Grandma Duck more familiar to each other, because the removal of Donald's nephews makes her a stranger in the story. In panel 2.5, Grandma refers to "that Gyro Gearloose", which seems to suggest a certain distance. To find an answer to this, it might be worthwhile to investigate if Gyro and Grandma have met before in a Barks story and how they met in later Barks stories. (Maybe there are other instances in which Grandma or other Ducks refer to "that Gyro" when his inventions cause trouble?)
Gyro doesn't call Mickey's nephews by their names, but this might be the same situation as when Donald's nephews were still in the story. In theory it might be possible that the story contained only two of Donald's nephews, but that would be remarkable as Barks always showed three nephews in his stories. (Or didn't he?)