Have been tinkering with original D&D rules and tried to compile easy mass combat rules for them (Chainmail is way too complicated for me and switches to non-D20 mechanic). Lot of inspiration from Godbound and Into the Odd game systems. Tried to use basic D&D mechanic as much as possible, just upping the scale and damage to unit size (damage is mostly done in HD not HP in that scale). So far it seems to be easy enough to use without slowing the game down too much.
For the sake of convinience I only used Ascending AC statistics (as I always translate my games to those). Should be easy enough to translate to descending AC, Thac0 or whatever system You like
It is still work in progress, and quite surely full of loopholes and typos. Hopefully I will add some easy domain management rules to this as well one day...
Feel free to comment and criticize

Or use, if You like.