You are probably aware of this, but ... some DRs are regulated for open sights. When adding a scope, the regulation may no longer 'work' and it may need to be re-regulated for the scope.

Some rifle's regulation will still function with the open sights and the scope.

Not an exact science.

One possible reason for swapping a Zeiss and instead using a Leupold, is the Leupold scope may be lighter.

If the scope has affected the regulation, they may have thought a lighter scope will improve the result.

If you can test shoot it, that will be a good way to find out. Make sure the bullets aren't crossing either.

With a scope to aid accuracy, 3 inches from a 9.3mm doesn't sound very good to me.

But if shooting moose, red and fallow deer, boar and similar sized animals, at 100 to 150 metres doesn't sound like a big problem. If shooting longer ranges, I would zero the scope for one of the barrels. Both will work at short ranges, one will work at longer ranges.

Some say the above is foolish, but it is practical too. Some old DRs had one barrel sighted for longer ranges too.

3 inches though for me is not the 40 mm you were told elsewhere.

I like that rifle. Would prefer it over a Chapuis or Krieghoff. Test shooting will help you make a decision.