I don't really have much of an opinion for 340s
Years ago when I had my first 74 duster, we put a 360 in it and it consistently beat my dad's 340 69 cuda. Only thing I can think is the cuda is an original and by then it had a ton of miles because my dad bought off a used car lot in 1972 and used it as a family car until 2004 when it got retired and replaced by a new Mercedes Benz
The 360 in the duster was a lot fresher but I think the 340 should have ran closer instead of being absolutely dusted