Kinda OT: Swan Mark I Linear expected output on 4-400A's in G-G?

[Bob, WB2UJD]

OK you amplifier gurus,

I have a Swan Mark I I have restored to mint condition and I am using 2
4-400A's in G-G in place of the 3-400Z's (3-500Z predecessor) it was designed
for.  It seems to work pretty well, but I am not sure it works as well as it
might.

What might I expect as a reasonable power output from such a combination?
Here are a few pertinent details:

3.75 MHz, just over 650W out with about 112W drive (not 100% sure of the
HM-102 meter cal)
The Mark I has an untuned cathode driven input.
2600V key down, 3300V idling, in operate (SSB) position
240 mA plate current
540 mA grid current (yes this is high, but tetrodes in G-G tend to do this)
90 mA grid current idling (bias)
Not 100% sure of metering cal either, but all metering resistors have been
replaced and are 1% or better.

DC plate input comes out as 624W.  Not sure how to calculate the grid portion
or if this contributes to total DC input, probably does in some fashion.

In Tune/CW position:
3.75 MHz, about 450W out with about 112W drive
1600V key down, 1900V idling
300 mA plate current
500 mA grid current
55 mA grid current idling (bias)

DC plate input comes out as 480W.

I am looking for some idea of how the amp is doing and what might be expected
of such an amp (Or how likely I am to piss people off if I were to attempt to
use this amp on SSB!).  This is my first linear in close to 30 years as a ham!

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