So as you may or may not know,there is actually a pilot chapter,or the chapter 0 or also called chapter 00 of Bleach.
It was released I think in 2000,but the idea was canceled.Only later when Tite changed few things,the manga was accepted by Weekly Shonen Jump.
The differences are,Ichigo looked different. Rukia looked a little different,but the main thing is that she shrinks in size when she gives Ichigo Shinigami powers.o__O There is no officers or classes in Soul Society,and instead of Orihime brother who comes to kill her in his hollow form,here it is her father.
There is also many other small differences,and also at the end of chapter Orihime dies.Lol,not really a spoiler,but still...xD
And yeah,Rukia is a part of third division,instead of 13th,and the zanpakous of Ichigo and Rukia looked different than they are.
If you are interested,you can read the chapter here,and you can see how history evolved.

Hmm,is this Ichigo.xD