> The eye is especially useful because the AGC action tends to increase the audio volume of a mistuned station, so the volume varies relatively little as the tuning knob is turned. The tuning eye was driven by the AGC voltage rather than the audio signal.

So, have a simple switch to disable AGC while tuning?

Or, a not-so-simple switch. The switch could be linked to a pawl which engages the teeth of a gear on the shaft of the tuning knob, such that you can't turn the tuning knob if you don't activate the switch.