I think he will show up with a pair a surprising amount of the time. We have a read that he is passive pre and post - this means that he is pretty likely to play a hand like 99 like this.
I used this range as an estimate of what he will _call_ a river bet with:
If this is the case, he has 84 combos you beat and 120 combos you lose to.
84: AJ(12) AT(12) A9(12) A8(12) A6(12) A5(12) A4(12)
120: A7(9) A3(9) A2(3) K7(9) Q7(12) JJ(6) J7(12) TT(6) T7(3) 99(6) 97(3) 88(6) 87(12) 77(3) 66(6) 55(6) 44(6) 33(3)
So check.