The only difference I know about between Zorro I and Zorro II is that you cannot have two cards on a Zorro I bus, only one.
BTW, Zorro I can be found on the A1000, and (backwards) on the A500. Zorro II is only found (stock) in A2000 series. Zorro III is found only in A3000 and A4000 series, the exception being one A2000 series computer that has Zorro III. I don't know if any of these actually exist though.