I'll start it. Not sure how much you're wanting to know though.
Gen I was the first small block chevy. Cubic inch started at 265, and went to 400 though the years.
Gen II was the LT1 and LT4. No rear distributor. Not sure on all the cubic inch sizes. Not to be confused with the Gen I LT-1.
Gen III. Started as the LS1. And I'll stop there, not real knowlegable off hand.
Gen IV. ?