Considering a '67 Dart GT Convertible as my first project. Am I insane?

Nice find. I also have a ‘67 /6 GT ‘vert, but it’s closer to Dana67Dart’s situation. Mine was pretty original and running pretty well; the 1st owner had it 45 yrs. Actually found the build sheet! If you do pull the trigger, get a service manual and parts list from my mopar.com. That’s an invaluable resource. There are a few NOS parts houses (AMS Obsolete; Len Dawson) and some decent repro shops. I agree with everything that’s been said about ‘67 Dart parts and 68/69 interchangeability, but don’t forget 67 Barracudas also shared a few parts and maybe 67 Coronets. Good luck!