Do you have headers? If so there may be a drop down bracket on the frame inorder to allow the slave cylinder to clear the headers. If it is not tight enough it will move from side to side. Also in some cases (as w/ mine) the previous owner may have added power steering and did not properly install the crush nuts for the bracket therefore loosening up their mounts. Then again it could be just as calpolymustang said, 40 yr old tech.
I've just started driving mine again recently and it takes some reacquainting on my part.
I used to drive nothing but older cars the last being the 'Stang then a '64 Falcon before that.
I had become accustomed to the newer cars during the past 10 yrs or so. Now I have to re-aquaint myself on the quirks of non-computer control, non-rack & pinion world.