I'm not positive on this but as a C&C design it's unlikely to have encapsulated ballast. Surely you've had the cabin sole (floorboards) up - you should see keelbolts if you do. In rare cases they are glassed over, but that's bad practice and not real likely.
If you can see bare lead, and the hull/keel joint then it's pretty safe to say it's a bolt on keel.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)