Help diagnosing rattle/vibration 1995 Ford Mustang?

I posted a question the other day about a rattle/vibration on a 6 cyl automatic 1995 Mustang which makes a rattle vibration when the car would be in gear (does not rattle/vibrate in neutral), and when moving up to about 20-30 mph. Lots of horror stories on the internet about Ford Torque converters. Today occurred to me that this vibration probably could not be U-Joints or bent drive shaft because in Neutral the drive shaft would not be spinning. Any experiences on fixing Ford torque converters without replacement of the torque converter? Cost of torque converter replacement would be more than the car could be sold for considering body damage from a rear end hit some years ago. Anyone have any opinions on transmission stop leak products for Fords....do they work?... do they damage transmission....