In my '72, I have been chasing a drive line vibration at cruising speed (around 2700 rpm). I grabbed the transmission crossmember and found that I could twist it. The crossmember rubber insulators look like they're shot (that's where the movement was). I have new ones on order from Inline Tube along with the hold-down brackets. I will get a new transmission mount just to be sure. With any luck, this will solve the problem. We'll see. My fingers are crossed.