The voltage divider resistor, R4 should be attached to the cathode150R node. I have found the cascode works better this way.

As in the pentode, g2 should be referenced to the cathode.

Other than that, keep the upper end of the load line running through g1=0 V before it starts deviating from the pentode-ish behaviour with its flat plate "curves".

Since the bottom triode is important for its gm, a triode strapped pentode might be useful. At 15 mA/V the 12BY7 and EF184 look nice. A step further would lead towards the 12GN7 at an advertised 36 mA/V and probably realizeable to 25 mA/V w/o the additional current source of the 25k resistor.

Looking forward to Chapter 6.
cheers,
Douglas