VOTT, indeed you can bypass the L-pad and let the horn run wide open if that suits your room and listening tastes. Some folks swear by installing a fixed resistor network to simulate the L-pad in their preferred position. Either option has it's advantages as well as disadvantages. I like to keep them the way Altec made them in most instances.

I "think" the networks in your 846A Valencias actually use a pot in a slightly different circuit instead of an L-pad, the whole mess is potted in a can of tar like stuff that you really don't want to deal with unless you have to.

Essentially "any" 8 ohm L-pad will work, i'd opt for a minimum 50 watt rating, 100 watts is what i think most of the stock Altecs were. If you can find "Violet" brand, you've hit paydirt. I've also pried them apart in the past and manually cleaned the wiper and resistive coil with some success on the large ceramic pads.