This is an awesome little game! I am looking forward to some solo dungeon delves!
Viewing post in Runecairn: Advanced Rules comments
Not specifically for Runecairn yet, but there are a good number of monsters for Cairn and guidance on how to convert OSR monsters: https://cairnrpg.com/resources/monsters.
I adapted Runecairn from Cairn so a lot of the principles are the same.