Holy cow, if you could find more on the proposed Omaha conversions, and the Wickes/Clemson ones, I'd love to see more. I've always had a soft spot for the four-stacker cruisers and destroyers, and would love to know more.
The Omaha-class stuff was... I think Norman Polmer, in his volume on U.S. cruiser designs, I want to say? It's been years since that book graced my shelves due to flooding (thanks, Sandy...), but I'm pretty sure that's where I came across that. Essentially, it would have been a twin-5" on each end replacing the twin-6" mounts, with the casemate guns removed entirely- where the upper casemates had been would have been quad-40mm mounts, although I wouldn't see any reason an open-mount 5"/38 couldn't work just as well there. I don't recall any of the other mods off the top of my head (torpedoes, light AA, etc.), but the other one that does stick in my mind is the removal of the tripod foremast for something more simple and less bulky to avoid blocking as much sky for the new forward 40mm mounts. Since by the time it was possible to start pulling these CLs out of service long enough for a conversion of this scale, though, it was because so many of thew newer Clevelands, improved-Atlantas, and of course newer DDs with their 5"38s, there just wasn't any real reason to waste the time on refitting these old dinosaurs. (I suspect a similar mentality is why the Colorado, for example, retained 5"/25s all the way to the end)
The 4-stackers, I honestly don't remember where I came across that, but like I said, none of that ever progressed as far as I know beyond the cocktail-napkin phase. The Navy lacked heavy ships (most of those were still being refurbished after a Hawaiian mud bath), but there were plenty of near-useless 4-stackers around, and leftover guns from when older ships were scrapped (12" from the Wyoming and prior, I assume it meant). Mount one fixed to one side, steam over to whatever tropical hellhole you want to land Marines on, and start thumping away. Inefficient as all hell, most likely- the fire rate would be awful, with only one jury-rigged gun and likely very little ammo to work with, but it beat nothing. But, luckily, an idea that batshit-crazy went away in favor of using the old battlewagons as they came back online- if a Clemson could fire a 12" shell every, say, 90 seconds (a number I'm pulling out of nowhere I admit, but there wouldn't be a standard hoist or any of that), and a New Mexico could throw twelve 14" every thirty seconds... why bother using up the shipyard resources on the DD idea? I'll see if I can find that reference again, but even back then it was pretty much a 'people got desperate for bad ideas, and sanity won the day' reference. I'm not even entirely sure where the gun would have been mounted on them, though aft seems as likely as any based on the Soviet and British attempts at the same.
