Just wanted to share a little prt scrn with you this is taken from a ZF internal program (catalog) this was given to me about 10 years ago (or so) and I have found it invaluable
What I would like to point out that with many of the on line catalogs they are simply relaying information that is given to them from Manufactures (Like myself or cardone or ZF) they are also selling parts
You will see that at the bottom of the page here it shows interchanges and you will find many tags that they are saying sell as the same part number this is why many web sites and retail outlets will sell all of the E46 racks as one part number (and paint over the tags)
Alex Really I have to say that all of my customers are of the utmost skill level Ha ha Just kidding I could not agree more that at times people have no idea what car they are even driving or what year or if it has tires. most commonly people will call and say they need a set (2) rack and pinions for their vehicle. So the fact that I did get a core back from a 323 with a 712 tag may have been a fluke or someone had changed the unit prior. when I followed up with the customer he had no idea and was not the original owner. he just wanted a rack that worked !
I have conveyed what I have seen as cores returned from customers based on what they purchased (years Models)
Below is a quick glance at the 712 shaft vs the 678 shaft as i Mentioned there is a slight difference in the gear (pitch of the gear) can I take a pinion from one and swap them ......yes !!!!!!
I am sorry I don't have allot of time today to make replies but thought I would post a little more info hope it helps