I'm in the middle of doing something similar to the premise of this thread. The current 340 with decent cylinder heads and cam in my '68 Dart kicks *** and runs very well. However, I'll be replacing it with a milder 408 because I don't need or want top-end hp for this car - though the 408 will definitely out-perform the 340, but in a milder package. The care is just a cruiser and I love the bottom end grunt that a stroked SB provides. The 340 will go into a future hotrod build.