if you really want to change the bottom bracket while spending a small bit of money...heres the trick i learned when i wwas converting my peugeot:
keep the stock french threaded cups and find an italian bottom bracket spindle. the french cups are thin, the italian spindle will make up for it. had one that was 68x110 and it worked perfectly.
or you can find a shimano un52 i think...or maybe 54. and replace the cups with phil wood french cups....a lil more expensive, but bomb proof.
or you can wait for velo orange like poguemahone suggested...but i was waiting for that to come out a year ago...by then i sold my french bike.