Would it not be a simple matter to somehow convert the 576 deflection plateAs mentioned already, the refresh is at 60Hz so a pen plotter cannot go that fast.
However. it should be possible to have the display "static" and have the plotter slowly do it's work.
But then you would have to design a mechanism to "follow" the "beam" at the slow pen rate.
That would be quite complicated.
In contrast, the spectrum analyzer is a single f(x) function to plot.
And in the case of my HP3580A which is a low frequency SA, the sweeping speed is very slow (can be a few minutes).
Indeed, what looks easy for an Arduino, may not have been in the 70s!