Stock is a 55W sealed beam enclosure. Many have upgraded to an H4 enclosure made by Hella, Cibie, etc. I personally am running the e-code Cibie's from danielsternlighting.com, and a prototype harness with 80W bulbs, and it is just about perfect.
After installing the harness and seeing the stock wiring, I would not run anything over 55W. If you want something that looks brighter but is still 55W, many (myself included) have run Sylvania Silverstars.