I stumbled upon Swords & Wizardry: FITZ’S VERSION earlier today as I was checking out some of the forums I frequently read. There are several differences between this house ruled document and the official Swords & Wizardry rules but the change that really caught my attention was the addition of the six sub-classes (Barbarian, Bard, Druid, Paladin, Priest, and Ranger) that “are not fully-fledged classes in their own right, but are designed as modules to be attached to one of the four core classes. They add capabilities to that class, and increase the amount of experience required to go up levels.”.
I have toyed with this idea myself on several occasions. I have yet to be satisfied with any of the systems I have devised; they have been a little rules-heavy for my tastes. I have put the idea on hold several times hoping to return to it and finally get it right. Fitz seems to have done it much more eloquently than all of my previous attempts. For all intents and purposes, this is basically a trimmed down “prestige classes done right” for basic style games! If you are interested in that type of stuff you should check it out.