[thinktreasure]

Yes, but you can have two coils with different static (DC) resistance that have the same impedance.  For example one may use a larger gauge wire which would result in lower DC resistance but have the same impedance.

Ok Bob, let me see if I can flush this out...

The 25A6G pentode  impedance at 400hz is 4000 ohms 
The original speaker matching transformer with a 1 ohm voice coil primary is 200 ohms (per Philco)
Divide 4000/1.25 and get 3200 or 3200:1
Take the sq rt of 3200= 56.6 and the output transformer for the original speaker should have a transformer with a 60:1 turns ratio
Since Philco calls out 200ohms  200/60 =approx 3-4ohms Or the original transformer would be 4ohms / 200 ohms

If I wanted to use an 8ohm speaker

4000/8.25 =484 sqrt= 22  or  a transformer with  about a 20:1 ratio  10/200

Does this seem right?

The speaker the chassis is connected  to now has a voice coil of about 1.2 ohms and a 500 ohm primary with a secondary of 1/2 ohm
So for the impedance to be right the secondary  should be more like 10 ohms?
So this speaker they connected seems to be not the right choice.

I have no idea how to calculate the needed choke value to replace the field coil.

To make this a whole lot easier I'm hoping to find the real speaker.