Here's a link to a thread on the S/SS board. Tons of great info there.

http://www.classracer.com/classforum/showthread.php?t=17876&highlight=D-Dart

Basically, if you get heads that flow as well, and intake the works as good, the same compression, and the same camshaft, a 318 should actually run better than a 273.

The 273 D-Dart is kinda like the Hyper-Pak Slant, more legend than fact.