I'd be curious to know what the history of the woman/car was as to why she had a demon just sitting in the garage, and all those extra motors.
If its got a /6 in it they did some work to get it in there, as its not a direct replacement for a 340 if thats what you think was in there originally. I may have missed it, but have you decoded the vin to find out what was in there originally or is the 340 just a guess (not knowing the history of Demons altogether...that may be a dumb question).
