I once flat towed a 73 Plymouth Fury repo from Hobbs, NM to Birmingham, AL with the engine idling. No problems with that part. Otherwise, it was a horror story.

I would modify the tcase shift rail to have a detent slot for the neutral postion, either by installing a m/t tcase shift rail, that has the notch, or by grinding a notch in the a/t tcase shift rail. This will require removing the tcase in either case (not terribly hard), removing the shift rail, and swapping it (I don't know that the m/t shift rail will fit for sure) or modifying it. There is a check ball in the tcase, there's just no notch in the rail for it to catch. This mod has been done before...