No Idea. I've never built one.
Having said that; this is a starting point.
I know the front end works because I've used it in a couple of other amps. There is alot of room here for experimentation. You can switch capacitors in and out of the first cathode to do gain and tone shaping. You can put attenuators between the first stage and the volume pot to control overall gain and harmonic mix. (this is really REALLY simple stuff). You can go to
www.duncanamps.com and download their tone stack calculator and play with capacitor and resistor values live to customize the tone stack. You can play with the gain of the recovery stage to control the mix between the harmonics generated in the preamp and the output amp.
I didn't include feedback but there are a couple of points you could tie into to do more tone shaping with feedback.
There are a couple of places in the circuit to try different kinds of resistors to add harmonic content. ( carbon composition are supposed to be non-linear)
Different 6V6s give radically different sounds when driven into clipping.
There are lots of output transformers to try, including the ones in All American Five radios. If you could find a tube radio that has a single 6V6 ouput tube and a power transformer, it would supply most of the expensive parts for this project.
BTW: A good way to prototype.
Don