What's my 340 worth??

Sounds like your getting advice from buyers, lol
I just sold my 340 last summer. It wasn't nearly as clean as yours and imo it was in need of a freshening up. it was connected to a 727 with a new 3200 converter.
I listed motor and trans for $3500.CAN
For 2 weeks I pissed around with lowballers, one guy tried saying he can get 340's for like $500. I told him let me know where cause I will buy them all.
2 weeks after listing I got a call from a guy up north. Sent him a quick video of the motor running, then he sent me a cert. cheque for asking price $3500

If your motor is in good running order I would think starting at $4500 wouldn't be out of range. Really there is no set value for a running 340, its whatever the buyer is willing to pay. I sold a bare 340 block last winter for $600 and the guy was thrilled. That engine went to the guy that owns those air planes on the TV show "Ice Pilots". He says they have all kinds of cars there but no parts to build them. I guess my point is, you can sell it cheap to your neighbour, or you can get what its really worth from someone who appreciated what you have.

Good luck with your sale !