[maxhifi]

Wouldn't it take something more like a triple GZ37 to make "a complete
one-tube high voltage high current bridge rectifier"?

I think he means one complete GZ37, and then another complete one with
independent cathode connections.

At least three
independent cathodes would be required, along with three rectifier
heater windings on the Power Transformer.

Not if the heater/cathode insulation is up to the task. If the EZ81 can
handle it, so can this super tube! Make it a 6.3V heater, too.