1968 Dart question....

I hate it when a thread derails and nobody answers the original question. :D

Anyways, the 68 Dart came with the slant 6, 273, 318, 340, 383, and 426 Hemi engines. As far as I know the four door model only came with the first three engines listed (non high performance) with the 318 being the largest. As has already been explained the 5th digit in the vin number can be decoded to tell you what engine was factory installed in the Dart.