IIRC, the 318s Getrag 240 could be used with the original transmission brace as it sits at the correct angle with the M5x engine, whereas the 325s Getrag 260 needs to have a custom brace made to deal with the additional angle as well as having the shift linkage tweaked for it to fit. Not sure on driveshafts with the 318 trans though.
There is nothing wrong with using either trans for the swap though. A 260 will easily handle the power you can throw at it... A 240 will take an S52 for awhile, but you'd have to be careful with it. My actual personal preference is for the 260 though. I might swap one back into my E30 because I hate the E36 getrag that is in there currently. I feel the Getrag 260 communicates much better, even though it is slow and clunky to shift in comparison.
Last edited by craz azn; 02-18-2013 at 11:42 AM.