First of all, I am a pretty new player and have been having some trouble with HU. My opponent has been playing super tight, and fit or fold post flop. I know that if he is willing to min raise the blinds he will probably call a 3bet here also so I am hoping to steal on a weak board.

Hero (BB): 151.6 BB
SB: 94.4 BB (VPIP: 32.31, PFR: 30.77, 3Bet Preflop: 9.38, Hands: 65)

SB posts SB 0.4 BB, Hero posts BB 1 BB

Pre Flop: (pot: 1.4 BB) Hero has 6c 5h
SB raises to 2 BB, Hero calls 1 BB

Flop : (4 BB, 2 players) 8s 7h 4c
Hero checks, SB bets 2 BB, Hero calls 2 BB

Turn : (8 BB, 2 players) Qh
Hero checks, SB bets 4 BB, Hero raises to 8 BB, SB calls 4 BB

River : (24 BB, 2 players) Jd
Hero bets 10 BB, SB raises to 54 BB, Hero ???

I dont see how I can fold here. 9-10 is well within his range but so are so many other hands like A8+, QJ+, 66+. I havent seen him overvalue top pair much, however, so that makes it more tentative.
Thoughts?