I'd just **** it and bet.
He obviously doesn't have the Qh or the Th that leaves A,K, and 7-3
He probably doesn't have the A or K because if he did he'd probably have a pair on the flop and imo lots of fish donk or c/r this flop with KJ and if they don't they often donk the turn with their acq. draw. Obviously not 100% but a great deal of the time.
As for the 7h-3h that leaves random As 7h type of hands and 5c 5h type of hands. Since there aren't a ton, and villain probably won't raise the 6h anyways, and he's too smart to fold his 6
6
I'd just say **** it and bet.
After about 15,000 hands of 6max between 1-2 and 3-6 I've basically decided to give up hand reading on the river, ignore all previous actions, and basically valuebet anything on the river that can get called by a worse hand ever.
It's worked pretty well.
I think our biggest concern would be getting bluffraised.