[Robb]

Re: the river bet

I'm trying to put him on a hand since he didn't raise preflop and called the flop and checked behind on the turn. I'm guessing Q5, K6, 86, type hands.
[Maybe a monster like flopped straight or 2 pair that didn't want to lose you on the turn but I doubt it since--- he shouldn't have an ace in his hand since he didn't raise preflop and you know that --- therefore a turn bet by him is good to induce a bluff raise on your part.]
I think it comes down to did he flop a pair?
So you would have to tell us whether or not it is likely he would have raised a pair on the flop. I'm guessing yes.

What can he put you on? Any flopped pair or straight draw I believe. Neither of you should have ace-high but there may be meta-hand stuff going on that may make an ace possible. So the straight draw would have to be:
A) 52, 58 or 68
B) Qx, Kx
and I'm not sure you would call 52 or Qx.

So what hands can you beat that he would call the river with? A bluff catching Q high/King high or a paired 4 or 3.

If he would have raised the flop with a pair then I think the river bet may be -EV. There's also possible he took one off on the flop and the 9 hit him. I would check-call for the slim hope it induces a bluff.