340 Build Spec's

For the last couple of days I have been looking around Ebay @ 68 Darts. The cars that I have found are sporting the 340 motors. In the build on my son's 68 Dart I do have access to that 318 out of the Challenger but its not what "Dad" wants for a power plant. I know it sounds stupid that I would want something different when the 318 wont cost any money execpt for the rebuild. But that is not what I want to put in his car...I want a 340...
I guess you could say it was a dad thing.. Now what I need to do is locate a 340...HELP!!!!!!

Thanks
Rick