Need advice: 318 or 340 for a 68 Dart?

Seems like Chrysler corp manufactured about 3,450,000 318 blocks between 1967 and 1991.

If you're looking for a 340, it seems like they manufactured about 12 of those.

318 can be had for about $150 or under $500 running and driving with trans.

340- just like buying a lobster at a nice restaurant- market dictates price.
(Hint- it's NOT $150-$500)

Dollar for dollar answer is 92-02 318 or 360 Mag, second choice 85-91 318 or 360 LA roller.