Back in the day - I'm talking sixties, seventies and into the eighties - when 340s were still relatively plentiful and inexpensive, it just made more sense to start with a 340 because it already had the good stuff in it. Whether considering just the motor, or the entire car. Hot Rod Magazine came to that conclusion when it built a 318 Demon project car that ultimately went 12's.
Today is a different world, of course. Not just the scarceness of real 340 cars, or 340 motors, but also the expense of either. Plus, there are so many aftermarket parts you can stuff into a project motor today that provide so much more performance than OEM that the stock equipment is going to be replaced for any high performance build whether starting with a 340 or with a 318. Or even better, a 360.
But I do miss the days when my Dad bought a two year old 71 Duster 340 with less than 20,000 miles for $1750, or when I bought a five year old 73 Duster 340 with 50,000 miles for $1600. I could afford that even on my then meager fresh-out-of-school salary.
(I won't mention the four year old Hemi Charger Dad bought for $1350.)