73 spool trans mount/ Drive shaft Blues..

Oldmanmopar said
Your drive shaft should measure 48 1/2 inches Center of U-joint to Center of U-joint with a 111 inch wheel base Dart. 108 inch Wheel base Duster/Demon are 45 1/2

I have had a strange vibration that is somewhat pulsating and increases with speed. In your opinion, could this be the culprit?