I would feel sorry for Naples in that case, since now they have neither the the long-standing intelligence and collaborationist apparatus of Genoa nor the overwhelming might of France, They would really have to depend on their British-backed and British-aided fleet and likely on British subsidies and on direct British support and that sounds like being constantly debt-ridden and dealing with potential bankruptcies and bread riots to me.
WI: Napoleone di Buonaparte, Liberator of Spanish Italy
How could they improve their economy? Maybe by export and extremely slow industrialization through the use of the coal from Brindisi Sardinia? They could've even traded Calabrian salt.
the sulfur in Sicily was hungrily devoured by Britain's growing industrialization but as a kind of early "Resource Curse" by having something so valuable to the UK meant that they constantly pushed for concessions and joint operations and sweetheart deals, they were always on guard to protect their interests and several times turned a blind eye to separatist or autonomist governments, forced on the royalists compromise and peacemaking when the conflict grew too interfering with their business, and straight up unleashed gunboat diplomacy on Naples. In effect the 19th century Sicilian Bourbons in their general ineffective flailing sprinkled with the occasional brutal repression and the odd attempt at moderation where Britian's pet sulfur-mining banana
Then could have Napoleon, supposedly taking the Neapolitan crown, have aided the coalitions against the french and traded to have austrian coal to industrialise or at least modernise the Two Sicilies economy.