Could my 340 block be filled?

You will not see a TS205 listed but it IS the correct sender for your car. I have been using that number for years as it is the correct OHM's. I used a NOS 1971 sender to spec it out and old books for cross referencing. Trust me, I had the same problem you are having. My temp gauge would read between 3/4-7/8 @ 200 degrees. With the TS205 it reads about 3/8.