on the classic strat wiring, the bridge pickup has no tone control anyway, which brightens things up.
i would probably try 300k pots in the first instance, i had good luck with that value on strats in the past. you can always tweak later.
on one guitar i did what dark blue murder suggests and used a 1M volume pot and added some parallel resistors for the single coils, that worked well and i think its a good suggestion.
be prepared to experiment a bit. you can do some very handy adjustments with pot values. you'll never make *major* tweaks, but if things are close to what you want they can make a useful difference.
