In my research for building a 5.9 into a 408 stroker, I read that the 340 is a preferred production engine for a stroker build due to its large bore and thick walls that can take a .040 overbore to make a 418 stroker.
This reference (How to Build Big-Inch Mopar Small Blocks) suggests that although its common to bore 0.030 over, the 5.9 should really only be bored to .020 over to avoid thin walls and distortion. Seems a little silly all the stroker kits advertised are at .030 over.
I happen to have a 340 from a 73 Duster, uncertain miles, but running when pulled. I don't plan to use it as I have a lot of parts for the 5.9 already that don't transfer over. So I'm curious regarding its value. I may consider having it tanked and magnafluxed if there's enough value there. I'm assuming the rest of the engine has no real value given that the 73 340 used a cast crank (shot peened IIRC).
A quick check on EBAY turned up a single very rusty 340 block for $900. Course he might be dreaming.