I used a 10 watt wirewound 0 - 500 ohm variable resistor in my 5F8A which I modded for switchable fixed / cathode biasing. Also those EH 6V6 are 14 watt max plate dissipation.
https://www.ohmite.com/wirewound/
I would lean heavily toward the G12H25-55hz as he bought them shortly after melting Claptons face when he sat in with Cream.... He probably asked Jim for some of those Amps that Cream had with his Middle name already on he front of them ;)