Phil,
I have to comment on something you said. The "builders" wouldn't use "whatever" was laying around particularly for armament when building the CLEVELANDS. Armament was "GFE" ... Government Furnished Equipment, and the USN determined what was delivered and installed. There was such a demand for 5-in/38-cal guns, for that matter there was a demand for ALL GFE, that their distribution and which units got what was controlled and not much was allowed to just lay around.
Differences in Marks and Mods are more "timeline" based on when the design for a given ship was finalized, when the ship was building, and what updates were being incorporated in the 5-in mount production based on lessons-learned.
The different Marks and Mods for 5-in mounts is a whole area for research in and of their own. Mostly the different Marks match up to the total WEIGHT of the mount due to the armor applied (or not applied) and intended receiver of the mounts; aka for battleships, cruisers, carriers, destroyers, etc. So many things determine Mod number that I gave up trying to figure them out. Heck even changing the housing to a different Mod didn't change the the Mark/Mod number of the mount!!! FLETCHERS have only a few single 5-in/38-cal mounts
Marks, but at least a couple dozen
Mods. From what I remember from looking at the twin 5-in mounts on Museum Battleships, I though that the armor was thicker ... not by a great deal ... than 2.5-in. One can really see a difference between a twin 5-in mount on a SUMNER-GEARING and a MASSACHUSETTS.
I didn't scan the late-WWII/Post-WWII Armament Summary pages for ALL cruisers when I was going through them, that would have provided a listing the Marks and Mods for all the cruisers.
What I did scan from a 1960 Armament Summary shows that;
Battleships
WASHINGTON, NORTH CAROLINA, SOUTH DAKOTA, INDIANA, MASSACHUSETTS, ALABAMA, IOWA, and NEW JERSEY had/have Mk 28 Mod 0 Mounts
MISSOURI and WISCONSIN have Mk 28 Mod 2 Mounts
Heavy Cruisers
BALTIMORE had Mk 32 Mod 0 Mounts
QUINCY had four Mk 32 Mod 0 and two Mk 32 Mod 2 Mounts
PITTSBURGH had Mk 32 Mod 2 Mounts
St PAUL had one Mk 32 Mod 0 and five Mk 32 Mod 2 Mounts
HELENA had Mk 32 Mod 12 Mounts
OREGON CITY had Mk 32 Mod 13 Mounts
ROCHESTER had Mk 32 Mod 11 Mounts
BREMERTON had Mk 32 Mod 4 Mounts
FALL RIVER had Mk 32 Mod 0 Mounts
MACON had Mk 32 Mod 12 Mounts
TOLEDO had Mk 32 Mod 11 Mounts
DES MOINES had two Mk 32 Mod 4 and four Mk 32 Mod 11 Mounts
LOS ANGELES had Mk 32 Mod 4 Mounts
SALEM has Mk 32 Mod 3 Mounts
NEWPORT NEWS had Mk 32 Mod 3 Mounts
BOSTON (CAG) had Mk 32 Mod 2 Mounts
CANBERRA (CAG) had Mk 32 Mod 0 Mounts
ALASKA had Mk 32 Mod 4 Mounts
GUAM had Mk 32 Mod 4 Mounts
ALBANY (prior to conversion) had one Mk 32 Mod 4 and five Mk 32 Mod 13 Mounts
CHICAGO (prior to conversion) had Mk 32 Mod 12 Mounts
COLUMBUS (prior to conversion) had Mk 32 Mod 0 Mounts
The few Aircraft Carriers still with Twin 5-in Mounts that I captured in my scanning
ANTIETAM had Mk 32 Mod 2 Mounts
TARAWA had Mk 32 Mod 13 Mounts
VALLEY FORGE had one Mk 32 Mod 3 and three Mk 32 Mod 4 Mounts
It would appear to be a good guess that the CLEVELANDS had various Mod's of Mk 32 Mounts.
Also, the USN continuously was upgrading mounts with OrdAlts to fix issues or to improve performance/safety.