Value bet 2pr on river or what - 3/6

[downtown]

Villain is 27/14 and RLY passive postflop. Not showing down garbage as far as I can tell. Bet this river to get value out of AK or what? Or am I only getting called by better hands?

Party Poker No-Limit Hold'em, $6 BB (4 handed) internettexasholdem.com

SB ($1073.20)
BB ($889.90)
UTG ($925.04)
Hero ($769.33)

Preflop: Hero is Button with A[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/heart.gif[/img]. SB posts a blind of $3.
UTG calls $6, Hero calls $6, <font color="#CC3333">SB (poster) raises to $21</font>, BB calls $18, UTG calls $18, Hero calls $18.

Flop: ($96) A[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/heart.gif[/img], 7[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, BB checks, UTG checks, <font color="#CC3333">Hero bets $81</font>, SB calls $81, BB folds, UTG folds.

Turn: ($258) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets $255</font>, SB calls $255.

River: ($768) 4[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, Hero calls $409.33 (All-In)