Based on your description, easily $50,000.00 to do a resto-mod on it and probably more.
Its not numbers matching, so the big buck value is already gone, plus it was a 6cyl.
Body off rotisserie, then modern suspension, ignition, fuel injection, transmission, steering, brakes, and so on.
I'd look for a totaled modern Challenger to use as a doner car.....come to think of it, my estimate is probably low....closer to $75,000.00 by the time you're finished, depending on how much labor you can do yourself.
The 440 may still be servicable, you'll have to pull it and tear it down. If it doesnt have a hole in the side with a rod sticking out of it, or locked up tighter than a drum, it can be refreshed.
I know a guy who works at a place not 10 miles away from me....you may have seen the place on TV......Restoration Garage.
They have an entire back room full of partially finished projects because the owner ran out of money