20-40 River Decision: Make the laydown?

[Jeffage]

20-40 at Taj. I have K [img]/images/graemlins/diamond.gif[/img]10 [img]/images/graemlins/diamond.gif[/img] and call after a few limpers in Mid-Late position. SB folds, BB checks. Flop comes A [img]/images/graemlins/diamond.gif[/img]6 [img]/images/graemlins/diamond.gif[/img]8 [img]/images/graemlins/diamond.gif[/img]. Ok, I like it. Check to me, I bet (yea I know, some might say to wait till the turn but this table is loose and people would call down with an ace no questions...plus the superman move is often a dead giveaway in this spot). Anyway, only the BB calls. The turn is another 8. He checks, I bet 40, he calls. The river is very ugly. A third 8. He hesitates and bets. Can this ever be a bluff? I'm getting about 6.5-1 but how can he not have a pair here? And if he flopped a lower flush, he'd prob check the river also or have raised the turn. Could you lay this hand down head up?

Jeff