Need to add adjustable bias to Sherwood S5000ii

Hi guys, I need to add adjustable bias to the S5000ii in order to accommodate the re-released Tung Sol 7591s (according to Jim Mcshane) as they're spec'd a bit differently than original stock. I can solder but I'm not good at figuring out the circuit. On my system page I've attached the schematics. I'm not sure if this amp would be considered fixed bias or cathode biased. I would like to add 10 Ohm resistors at the cathodes in order to measure voltage drop and calculate current flow. But I'm trying to figure out where to install the pots for bias adjustment. Would I install them on the cathode prior to the resistors I mentioned. Or would I replace the 6.8 ohm resistors (R45 and R85 on the schematic) with pots. Also there is this "output tube balance control" aka R5 on the schematic, which is actually a dual pot on the back of the chasis. I'm wondering if that is some sort of a poor man's bias which I can use. I've also attached a snapshot of the description in the manual of this pot on my system page. Typically would you have one pot for each power tube or would you just bias them in pairs? Sorry for the elementary questions but I'm new to modding circuits. Thanks