lft has a pint there .. if the front universal is going it will shake the tranny and motor and sometimes make if feel like the front end .. I had that problem in a 68 Stang and when I crawled under it the front universal was about to fall out so I changed it and the shimmy was less but still there so the next idea was to rotate the driveshaft 180 degrees and that solved the problem. Don't know if this is your problem but it's worth a look and looking is cheap. Also if you have to change it get one with a grease fitting .. my original one didn't have one and that was part of the problem I'm sure.