+1 go get a Rubbermaid tub and put the rock in there with a powehead and a Heater.
I just started curing a bunch of dead dry rock my uncle had in his garage for 2 years. For the first fill up I used the tank water from my water change. I'll do 100% water changes the first few times and rearrange it and inspect it.
In a month or so, when ammonia and nitrite is zero I'll put it in the tank and sump
With yours since it is already partially "alive" I would inspect it closer to see what hitchhikers you may have.
This is the tub I used its 22 gallons