It truly is JUNK. There are plenty of 340 manifolds out there. I sold a very nice one about 2 years ago the third time I listed it for, I think, $125. The first two times I listed it I started heard nothing.
FWIW, Take the loss and move on. It's like this. If you had a 69 Roadrunner with the Matching number 426 Hemi in it, and the Hemi had a lot of freeze crack damage that could be repaired for $8,000, then spend the money. You have a part that is not at all rare. Place an add in the parts wanted section.
