The first tweak is magic. In the first city of Kanebok, where the setting is centered, magic is simultaneously queer and yet woven into daily life. Magic isn't a single thing. There are different kinds of magic. But wizards - those who master otherworldly powers and ancient spells - are not trusted. They are not natural. And hanging over the entire city is the belief that the four greatest wizards from the time of the wizard war still linger in some kind of quasi-living state, subtly affecting the living world with their unending machinations against one another.
(See, that last paragraph was meant to be a discussion of how the magic rules differ from standard OSR rules and yet all I talked about was the mythos of the setting.)
Wizards in this setting would not be limited arbitrarily by spell slots and number of spells allowed per level. Instead, they would acquire their magic however they can. It's an organic process. Players would seek out magic and once they find a spell and figure out how it works, they can cast that spell as often as they like. The limiters would be in the cost of the spell. Each spell would be described in a bit more detail in terms of how it is cast so that spell components, casting time, and other costs are baked right in. There is no need for spell slots when you have to sacrifice blood, treasure, money, or soul to cast a spell.
(Frankly, this is how I'd like to run ALL my D&D style games.)
The only other rules tweak I had in mind was to use the attack values table as a basic rule for all mechanics. I posted about it here. I still think that's a boss idea, but I just don't know if it's boss enough to justify using it here.