The "Magic Eye" is unique facet of vacuum tube history, so I would keep it.
To drive a meter requires an extra current amplification stage tapped off (sampling) the AVC line.
Phil-AC0OB
If it's so "unique" why did Gonset get rid of it with the Gonset III? Unless the plan is to use this 60+ year old piece of equipment as a museum piece
mods (with hammer, chisel, drill, iron, etc.) might make this thing more useful.
A 6J6 or 12AU7 can easily implement a S-meter circuit. A germanium diode to sample the RF output can also be used to get a relative RF output reading on the meter.
Too many "museum" or 'shelf queen" equipment collecting dust all over the world. People reliving their youth
or the way it was back then(whenever), but, in reality you can't go back no matter how hard you try!