I think that the mod may be to implement the 6G3 http://bmamps.com/Schematics/fender/deluxe_6g3_schem.pdf vol, tone and mixer resistor arrangement, using a dual gang pot for the tone control, such that the one tone knob adjusts both tone controls.
The downside being that the channel tone controls aren't independently adjustable; unless a dual concentric pot was fitted, but then you'd likely have to lose the chicken head knob for a dual concentric type.
I know its based of 6g3 I'm just not 100% sure how to do it. I'm not sure if I go from the two 220k mixing resistors to pin 2 of the v2, thats where i'm confused. Thats why I bought the kit so I know it would be right.
I did that mod on my 5E3 a long time ago. I may have the instructions out in the garage. I'll give a look see and post if I find them. Bruce Collins is incredible about giving advice over the phone. Your best bet is to give him a ring.