I decided that rather than struggle doing conversions of various retroclones / neoclones, I might as well just write another one (the first one was Microlite Iron Heartbreakers). Here it is: Into the Depths. It's free for download and you're welcome to modify it however you please.
It's a chassis that I'll be building off of and using for Necrocarcerus and other fantasy campaigns, loosely inspired by the size and rules minimalism of Searchers of the Unknown and Into the Odd, with bits and pieces of my favourite house rules in it, and based off my experience using various versions of Swords and Wizardry. It's meant to be easy to plug material from other games into - my become-a-wizard rules for it will be some mixture of Wonder and Wickedness with the spell research rules from Crimson Pandect. It's classless, with minimal stats to keep track of, and is almost entirely the player-facing elements of the rules. I stuck in an upgraded version of my leveling rubric for the Black Hack, since that seemed popular with folks.
Anyhow, merry Christmas and enjoy!