Differential 740 750

Are the differentials from the 740 and 750 easily swapped?
What is the best upgrade for the 750?
What is the best way to find a good quality used one?

Any other advice?

Thanks

Here's a link to a guy who knows a lot more about these things than I do. I know he replaced his automatic transmission for a manual but I don't know if replaced the differential or not. I believe the site includes his email address. Good luck.

http://www.nmia.com/~dgnrg/page_2.htm

Search Jeff Wong on bimmerforums.com he has a 750 and has "done it all"
a rear end runs 500-1100 for the unit itself.
It really depends on how you drive the car and what you expect. Diffs. will get you off a touch faster but drop your top end. Air induction helps if you have cool air around. Supercharging really helps.