Well, I guess what I mean is the most stripped down version of published 5e. I know they provided guidelines in the DMG for what would make a good 'OSR-like' experience (not sure exactly how it was presented, I've only skimmed a lot of the 5e DMG and it was a while back). I mean isn't there a defined subset that eschews HD, uses just the basic 'big 4' classes, doesn't include any of the fancier subclasses (particularly the half-casters), etc? That also lacks skills, the proficiency system, MCing, and probably a few other things I'm forgetting.
I would think that would produce a FAIRLY reasonable emulation of B/X, but with modern AC and such things. I guess character's hit points would be a bit higher, but damage output would mostly make up for that, wouldn't it? I mean things would be slightly less deadly at a level of literal translation of elements from say "Caves of Chaos" to that version of 5e, but you'd just tweak things slightly if you wanted it to be equally arbitrarily brutal.
I mean, there's nothing terrible about the core rules of B/X, but they ARE a little antiquated, with descending AC, attack matrices, and the oddly arbitrary saving throw categories (as examples). It would certainly be easier to teach to 3.x and 4e people (and 5e people) than teaching them a new and somewhat quirky engine.