I did some rough calculations in this spot.
First of villain can't be that good because he bet so small OTR. He should be overbetting or at least potting because you capped your range pretty hard after you checkback turn and bigger betsizes allow villain to bluff more combos in theory.

Therefore he is either underbluffing or overbluffing here because he clearly can't be playing optimally.

There are like 30-40 combos that beat you and he can turn T7s, JT, QJ into a bluff so in theory he has to be overbluffing here for us to profitably call HOWEVER he might valuebets lower flushes.

So it's crucial to know how many lower flushes he has here. If he defends 63s pre for example I'm definitely calling this river because there is a good chance that he bets a lower flush on this river and there gotta be some in his range plus the fact that people will bluff T7s and JT at a somewhat decent frequency.

If people at NL50 don't defend wide enough I would fold if they don't overbluff on the river.

idk if not defending hands like 63s is incorrect. Cant see that being a profitable call pre with rake.

I don't know either but I took pokersnowies defending ranges as a baseline and I think Kalupso wrote that snowie is making rake considerations.
Now 63s may be too thin of a call but I can imagine that people defend 75s 54s 64s and if they valuebets those OTR it's probably fine to call the river as played.

But one thing in the hand which we haven't touched yet is why you decided to checkback turn. You have a straightflushdraw, I'm always betting that on this turn to put pressure on his toppairs.

the 8 hits villains range a lot. I have no 8x in my range when i bet this sizing otf.;
;
villain can xr which would suck bc my outs might be tainted otr

So you think that he is bluffing every QT, JT, T7s, 67s? In that case we could be calling with K high and feel good about it...

I don't think we can assume that villain bluffs with those hands everytime. But I don't think we can assume that he never bluffs with them, either. So I'd assume it's somewhere in between.

I don't know how often villain has to be bluffing exactly for us to make this call, but combining the possibility of him bluffing with those hands and the fact that we beat some value hands makes it more of a call than a fold in my mind.