Another problem is that 85662A display uses 2 vector modes, a slow one for slow sweep (digital storage) trace, grid, readout and a fast one, that is in use when using the bottom box in downconverter mode, with zero span.
Then the vector display is used more like a analog scope with up to 1MHz, depending on the video bandwidth.
With a slow vector display, you loose the downconverter scope mode. Don't use that one much, but I guess that's why they used a vector/scope CRT instead of a magnetic deflection monitor CRT.