Some motos are swiss threaded in the bottom bracket, which makes removing the fixed cup an adventure, and replacing the BB even harder. If the cups look good, keep 'em. You may have to change spindle length, tho, depending on your crank manufactuerer's recommendations. Info on older French bikes located here:
http://www.sheldonbrown.com/velos.html
Note there are several sizing/threading issues besides the BB.
Suntour made pretty nice bar end shifters, should be able to find 'em on ebay. I believe the bike you have could be a nice beater/rider, but like Walter, I wouldn't go overboard. I would check to make sure the rims are alloy, at least.