What's my 340 worth??

If it was me, and given it's a real Formula S - stick the driveline in the garage and forget you own it. When you're tired of it, having that engine, even if it's not in the car or has run in decades - will make thousands of dollars of difference. It's not like a GM product in theat regard. mopars are ultra rare compared to any Chevy that doesn't have COPO in front of it. so you really, really REALLY want to keep it with the car, even if you go LS or Coyote.