If you are going to add a preamplifier, why stop there? Replace the whole cheapie amplifier with something decent. Even a modern headphone amplifier might do it.
If you want to preserve the antiquity, to restore it, you will have to find a proper cartridge. Rochelle salt is the material that was used for the most part; there is a web site that shows you how to make your own.
http://blog.makezine.com/archive/201...rew-piezo.html
http://www.seawhy.com/xlone.html
http://www.seawhy.com/xlroch.html