PLO25, River bluff catch?

No, he will have a flush or maybe even hit a full house (with kings over ** or if he hit a set). Don't expect a such deepstack try to bluff you.

I'd rather bet turn. If he calls, you can check behind river. If he raise, it's an easy fold.
Many players will call turn with an oesd or flush draw, so you can see it as a value bet.

Look like an easy fold on river

Villain might well have aces preflop and choose to slow play or indeed have the king once he calls the flop. I certainly don't mind a turn bet since villain could also float this flop knowing you slow down with your bluffs on the turn and bet again with a king.

Bet $4.50 on the turn (Which I would also do here with KJxx) and fold to any aggression. If you check this turn expect villain to barrel into you on the river with 100% of his range (and you have to fold).

So your turn range has to either be to check the nuts on the turn for balance or bet your air and semi bluffs. Choose one and stick to it.