I assume you're referring to loose balls vs modern sealed cartridges?

Yes, you can replace it with a sealed cartridge, with the caveat that your Peugeot is French threaded, and will require a French thread cartridge. Fortunately, Velo-Orange recently came out with one; before that you would have been SOL: http://www.velo-orange.com/grcrufrthbob.html

If your bike has a steel, cottered crank (1975 means this is likely) you will need to replace the crank as well. Any standard square-taper arms will fit on the Velo-Orange bottom bracket.

Otherwise, if you're on the cheap, just buy new balls for your existing bottom bracket, and ride and enjoy.