I'm trying to hack together some Over-The-Top Encounter By Dungeon Level Tables utilizing the material from all of the OSR Monster Books I have (The Swords & Wizardry Monster Book; Monster of Myth; Malevolent and Benign; and The Tome of Horrors Complete).
However, whereas AD&D/OSRIC categorizes monsters into a scale of I through to X for "Dungeon Level", Swords & Wizardry utilizes a Challenge Level scale that is analogous to the monster's hit dice, but adjusted for special abilities, so it's a more granular and also an open-ended scale.
In the 1st edition Dungeon Masters Guide, in Appendix C: Random Monster Encounters on page 174, there is a table for determining appropriate dungeon levels for random monster encounters by use of it's experience value, such as III: 51-150 X.P. and IX: 5,501-10,000 X.P.
Obviously it's easier to convert from the more granular and open-ended Challenge Level scale to the restrained and smaller AD&D scale.
Now, as previously mentioned, the Swords & Wizardry Challenge Level is determined by a monsters Hit Dice (with adjustments for special abilities), so what I did was use the Experience Points Value of Monsters table from page 85 of the Dungeon Masters Guide to determine the "Dungeon Level" of a monster of average hit points and no special abilities for Hit Dice of 1 through to 21; after 21 I had to use some fancier math to determine at what Hit Dice an unspecial monster would need to Break the Dungeon Level X threshhold (31.7524 Hit Dice).
Interestingly enough according to this scheme the only monster in the Swords & Wizardry Monster Book that qualifies for Dungeon Level X is Orcus, Demon Prince of the Undead, which is actually in line with the AD&D tables. All of the CL 32+ monsters in the Tome of Horrors Complete are pretty much in line with the over-the-top nature of Level X AD&D Dungeon Monsters as well. When comparing some S&W version of monsters and their CL to their AD&D analogues and their Dungeon Levels they either match up or are off by 1 level, so this system is close enough for me.
S&W Challenge Ratings by AD&D/OSRIC Dungeon Levels
AD&D - S&W
I - 1
II - 2
III - 3,4
IV - 5
V - 6,7
VI - 8
VII - 9-14
VIII - 15-18
IX - 19-31
X - 32+