Hi Shag,
I was thinking of doing the same thing for my Valve Junior but wasn't sure where to get the In Wall Attenuator, so thanks for the link! However, I can't answer your ohmage question.
Have you asked anyone on the message boards of
www.epiphonevalvejunior.com? (I think thats the address...)
A number of people were discussing using it as an attenuator on there.
I've recently soldered in some mods I bought of EBay into my EVJr Combo and have been very pleased with the results.
It's still too damn load though!
Good luck for you search.
B