Giving Up?

Lets see, off the top o my head (and I think 67 Dart 273 mentioned this) The pilot bearing, when you swapped from auto to manual did you address this issue? if the engine had an automatic crank, the pilot hole would need to be drilled and drilled correctly, then a pilot bushing would need to be installed. If this was not done correctly, the input shaft could be constantly spinning or binding in the hole in the back of the crank. If the pilot hole was not drilled, the only other thing that could have been done is swapping the auto crank for a manual trans crank with the pilot hole drilled from the factory. Not sure if this issue was addressed, it may be overlooked if a transmission installer didn't know about it. there are things about these cars that are just the way it is, just cause its old don't mean its easy to work on :)