[sirlurkalot]

If Billy's not tilting, the action screams QJ. If he flopped a set, I think he'd c/c the flop & wait until the turn to raise. If he's tilting, KQ or a small flush are also possible. Normally I wouldn't expect him to three bet the draw.
I've seen him many times hit the breaks holding straights & flushes whenever the board pairs. Still, I like the river bet, and would anticipate a call w/QJ more often than not. You bet could also occasionally get him to throw away a better hand such as AJo.