The Heising choke removes the dc from the output side of the modulation
transformer. The DC saturates the core and reduces fidelity.

This circuit is not common in ham gear because of the additional expense,
weight and cost - but it was common in broadcast circles.

I would make one change to the 813/811 circuit. If you load the grid down
with fixed resistors, you can remove the need for neutralization. You would
load the grid side of the circuit enough so that full power from the exciter
(a Ranger I recall)) would just drive the amplifier.

More sensitive tubes can get away with using a 50 ohm resistor and no tuning
on the input. That would probably not result in sufficient drive (I have
not worked with the numbers). However, you could use something like a 300
ohm resistor to load the grid then use a 4:1 step up broadband transformer.
One less control. One less potential for overdriving the amp. No
neutralization.

73, Colin K7FM