HeY OT:

I would use cascode mosfets 'cause that's the only way to eliminate the Miller effect they used to make valve tuners that cascoded triodes then they invented valves that could get around the miller effect so no more cascode triodes
IMO you could use matched GaS fets on 7pin or 9 pin valve plugs then in that circuit your going to have to transform the low output impedance of the fets to the high impedance out of the valves with a small toroid transformer
and bias the gates properly

73 de n8zu