They're about the same size. The Ju-52 was okay for its time, but I don't think it could carry much more than 10-12 paratroops. For the sake of this game it has to be 10 or less.
Hitech has said he can increase troop load to anything, but even if he gave us 1 plane that could carry 30 troops, he'd just up the map room requirement to 30 as well.
Leave it at 10, if ever included in AH. The defensive guns make up for the slower speed.