Well, I would stick with the "basic set" cape gun and extra shotgun barrels.
Purpose: to have "all you really need" in a handy package, in Europe.
Extra rifle barrels (probably with scopes) make the package bulky, expensive and are not really needed.
My secondhand Merkel combo is fine as it is, but when building new I would change some things:
- shotgun should have 30 inch barrels
- the whole thing with 16 gauge shotgun barrels - yes I know 16 ga is extinct in Europe but 12 ga barrels make the whole thing heavy and bulky
- a more compact scope