Just to save time, I gathered a list of classes and levels that have pets that can proc this sword. I'm not promising 100% accuracy, but it's what I found.
Beastlord Level 54 (Level 41 Pet) **forums.beastlords.org**
Magician Level 49 (Level 41 Pet) **eq1.eqsummoners.com**
Necromancer Level 48 (Level 41 Pet) **Posting from Allakhazam**
Shadowknight Level 64 (Level 41 Pet) **Same spell as the Necro**
Shaman Level 61 (Level 58 Pet) **Posting from Allakhazam**
Enchanter pet: I couldn't lock down a specific pet that bordered the Level 40 proc mark. However a post about the level 62 pet spell claimed that it summoned a level 58 pet. I'd presume you'd be safe with one pet lower (the level 55 pet). Not a lot of info about enchanter pets is available, unfortunately.
Note: Previous Shaman pet was level 39, just under the legal limit!