How much would you pay for this 340?

I have not seen a $500 340 block for a loooong time. Regardless of what everybody thinks the external look is worth, a 340 core is still expensive. Just go look in the mechanical parts for sale. Do I have dollar value? Not without seeing inside, but I bet it ain't $500 for the block and J heads.
You would if it was .060 over and worn out. I wouldn't touch it without pulling the heads and pan. The pan doesn't bother me. My '70 340 had a truck pan on it when I bought it in the early '90s. It also had a BIG solid cam and W-2's. I did buy it from someone I trusted as well so I didn't feel the need to pull the heads.

Oh, that engine with less than 10,000 miles was $750, which was a bargain even back then.