Its a 1978 320i Canadian Car what is the rear end gearing and what can it be changed to? Who has changed it? any input?

I'ts a 3.64:1

Change it to a LSD in any form if you wish, the common swap is the 3.91:1, most of us here have done it. Its a direct swap no tricks needed

...as long as you get a diff from an e21 that is.

There are all sorts of BMW diffs out there, but if you are looking at 3 Series diffs, the e21, e30, and e36 diffs are NOT interchangable (for the most part). Just make sure the diff you are trying to buy came from an e21. There are ways to swap just the gears, but since most diffs don't go bad, it is usually easier to just buy a diff with the gearset you want.

3.91:1 would be great, as long as you have a 5spd (or maybe an auto). I would think that the 4spd would just be WAY too high up in the rpms most of the time on the highway....but I haven't driven a 4spd with a 3.91 yet either, so....

well wrapping it past the 220 was not tooo hard I will give up some top end for low end.