You know, if it's at all like my Chevys that I had from around the same
time, there is a clamp that rides against the tube in the engine
compartment that keeps that from happening.  I have seen lots of them
where this tube (plastic or something like that) has worn and the clamp
must be loosened and moved up to remove the play.  That may or may not
be a pretty permanent fix for the problem.  But that worked on my 71
Vega, which shared a lot of technology types with other Chevys of the time.