If it is painted grey, then it is a dynamo. If it looks like a miniature car alternator, then it is the higher output alternator. They are relatively easy to install, and if you do a search, you will find some pictures and text as to how to do the installation. I don't know the current price, but they were about $80 a few years ago. The directions that come with it, are not the best, but it is relatively straight forward.
Dusty