I'm helping a buddy start a 69 Dart build and he has a 340 short block that needs rebuilding. I was wondering since he still has no heads, should he sell the 340 and get into a 5.9 magnum for the heads and roller block? The Dart is run-of-the-mill, so originality is not his concern. His concern is good power, drivability and longevity. If a magnum is the way to go, which years should we look for?

Thank a ton for all your input as I have no experience with magnum engines other than the 5.2 in my 99 Durango.