[DavGoodlin]

Excellent question

If I had to guess, I'd say that most 1950's-era converters were intended for little more than reception of low power UHF and translators serving a limited, line of sight radius.

The Mallory I had was not very sensitive, often worse than a bult-in tuner. A few rocks between me and the Philly transmitters 45 miles away made it hard to get decent UHF without a rooftop antnenna AND a UHF mast-mount pre-amp.
If you were one hilltop away from the UHF transmitter in the old days, you didn't count for being in the coverage area. In those days, a 500 kW UHF channel was unheard of.

I have several Blonder Tongue converters from the 60s that seemed to work as good or better than a factory-installed UHF tuner. They still were hashy if there was a strong local UHF channel.

6AF4 was connected as an oscillator , using an 1N82A diode for a mixer, didn't a factory UHF tuner also lack the RF amp stage?
All VHF tuners had a true RF amp, a stage of amplification between the antenna and mixer stage. This same stage was used to amplify only the IF output of the UHF tuner, after the noise was added, not very helpful.

I have never seen a tube booster for UHF either.