According to the contributor "01A" over at Audio Asylum, this is the formula for the Zout of the Aikido circuit:

Zo=(rp/mu+1)+Rk||(rp(mu+1)Rk)

I calculated the Zout of my variant to be approximately 583 ohms, using these values:

rp=6050
Rk=325
Mu=20

This calculation will be useful in trying to design a phono preamp around this circuit, which is why I was curious.

I think I may try to do an Aikido phono, maybe using a 6N1P as the first tube.

-j