This is my opinion for what it's worth........
The car has rust issues under the vinyl roof, apparent bubbling on pass side and swelling at the seam on driver's side.
It also has bubbling in the paint on the lower driver's side quarter behind the rear wheel, as well as bubbling on the bottom of the pass. side front fender between the door and the wheel.
Any rust bubbling means holes underneath when you get the paint off.
The car has the incorrect grille in it, the correct shark's tooth grill will cost you upwards of $1000 to replace unless you get lucky.
The under hood wiring is not good and needs to be gone through. I hate the upper alternator bracket!
Incorrect paint under the hood and in the trunk area makes me wonder what it's really hiding.
The rest of the car looks okay, it has the right year rally wheel center caps and painted mirrors on it.
The engine? Who knows what it is without the numbers off it, as for parts like oil filters and usual wear items, they are the same as a 318.
If it is a real 340 car, it would have an 8 3/4'' rear end in it too.
The 340 wedge decal on the hood is incorrect for the year but looks good.
Check the numbers out, and if it is a 340 car with a 340 in it and it runs and drives good, i will go out on a limb and say it's worth about 5 to 6 grand as it sits.
If nothing else, it LOOKS pretty good.
Also, what are your intentions? Buy it and enjoy it as is and restore it in the future?
It would take a lot of work and money to restore it after you get into it, remember that.
Ask the guy, why is it for sale?
I honestly think he's selling it before it gets worse and he has to put some more money in it.
If you are looking at it as a labor of love, not an investment, this could be a good car if the price was right.
Good luck and let us know what happens!