Extended service life GB.
Modify subject for service years past when it was in regular service.
Likely won't be a effective as completely newer planes-ships-armor.
So what --- gets modernized as best it can dependent on how many years in future its service is. 10yrs? 50yrs?
Jet powered DC-3. F404/414 powered sidewinder/AMRAAM armed F-94. Newer guns, sensors, turrets on armor. Reactive armor on M3 Grant. 1990s King George/Bismarck. WW2 USS Olympia. 1930s/40s Martin MB2/Vickers Vimy. 1960s/70s Lancaster/B-24/Betty/He177.
Cold war/Gulf war/2015 USS Arizona (USS Olympia?).
So on and so on.
Bit of tongue-in-cheek character to a build is OK (fun).
ALCM toting B-24, Elint/ECM Wellington, Ford Tri-motor gunship,,,,,,