To add the feel of a tech advanced kingdom without just turning it into the wild west, try adding an elevated train system the players can utilize, give an NPC a clockwork familiar, and swap stagecoaches and horse cabs with mechanical variants.
Use Fantasy Craft which has good firearms rules and a double barrel 'tech level' system. To represent new advances being made all the time you could do something like this:
Era: Reason (this captures the time period your using as inspiration)
Reason era gear (including firearms) is limited to complexity 10 items (all items have a complexity and ERa listed) unless the PC makes it themselves.
Every game year add one to allowed complexity for common goods (11 at year 1, 12 at year 2, 13 at year 3 etc.). The technological background of your campaign will advance in a way where it is clear cut from the rulebook whether an item has been invested yet.
Fantasy craft even has ways of modifying equipment to represent prototypes (eg. crude materials) to raise or lower item complexity.
And its a nice cimenatic system that's easy to play.