This is arguable. The Ju-52 used an old version of the BMW 132 engine (used carbs for one thing?) and an older form of cylinder fins?
The newer version/s of the BMW 132 used fuel injection and came with a choice of 3 different supercharger gear ratios. If you were not interested in high altitude (10,000ft) you could get into the over 900hp range.
The difference in effort to manufacture should be small, depending on the fuel injection.
The Bramo 323 might be able to use similar machinery although castings/forgings would need to be changed over. That can get you to 1000hp per engine.
Swapping a pair of 960-1000hp 9 cylinder radials for a trio of 725hp 9 cylinder radials might be doable.
When is this likely to be done, is the issue and when do you stop production of one engine and begin the next? And what impact does this have on existing deliveries? This is the point I'm making. All of this seems like a lot of energy for little gain, especially since the LW never specified a need for a more advanced Ju 52 in the first place. The aircraft's performance might increase, so how does that affect operations? Can it still operate into smaller rough strips with retractable gear and a higher landing speed? How does this affect its load carrying capability?
We are talking about a slow transport here, an increase in speed probably won't offer a sufficient change in its capabilities.
This entire argument is being driven by this notion that EVERYTHING has to be all-metal with retractable gear and modern construction to be of value. None of these changes are going to make a better Ju 52.