needing help

Lets start with the basics. I have a 68 barracuda, 440 4spd. It has an 83/4 rear end and dart disc brakes up front ( I was told when I bought it) with the bigger torsion bars and sway bar.
Now on to the question. It seems when I push in the clutch, to shift gears. I have some wiggle, I'd call it. The harder the acceleration the more the wiggle. Any suggestions or ideas what would cause it, and or fix it. Thanks.

Jon