I'm fine with the current possessions of chimes, mithral shirt and spell pouch.
So for the "In life" bit we, as usual, have little to go on.
Presumably he was keen on religion when alive, being a sohei who haunts a shrine.
The Keeper is Neutral Evil, so is there anything we can infer from that? That he wasn't that committed to ideologies?
At 11th level the Keeper was the second highest level of the Swords, with only the 13th level General beating him, so maybe in life he was a bit older than the other swords, perhaps in an "elder statesman" or "semi-retired leader" role?
The original encounter had a swarm of carnivorous beetles hidden in a pit underneath his shrine's altar. They would boil out and attack the PCs if they found the secret catches and moved the altar to access the next part of the adventure. Maybe mention something about carnivorous beetle swarms in the description?
Or we could just leave it simple and not say much so we don't have to invent anything that wasn't in the original adventure. It doesn't even give him a name!