75 Spot vs. Paired Door Card

[Jeffage]

This happened a couple weeks ago in an Atlantic City 75 stud game. We were seven handed and four players (no cards higher than a jack) limped - this in itself is pretty unusual. I'm next with the (4x 5x) 3x and toss a quarter in. There are no deuces or sixes out. A loose player with a king up calls behind me.

On 4th street, the loose player pairs kings. He bets the full 150 and everyone folds to me; meanwhile, I catch a six and no one catches a deuce or seven.

4th Street

Villain: (x,x) K K

Hero: (4x 5x) 3x 6x

There is $430 in the pot after he bets, offering me immediate odds of just under 3-1. Also assume that this player would NEVER (or at least almost never) limp with kings on third street even though it would probably be correct to do so with the way the action presented itself. So his likely hands are: kings up with a small pocket pair or dry kings with middle side cards. This player also has been known to make "bad" late street folds because he "knows" he is beat. What is the best way to proceed with this hand?

Thanks,
Jeff