The e28, e36 compact & Z3 uses a similar case to the e30, and you can swap them all around relatively easily.

One thing you might want to look at for extra diff cooling is using the Z3 M coupe / M roadster backing plate on the diff as it has large cooling fins on it. See here...

http://forums.bimmerforums.com/forum/showthread.php?t=1017244

The other medium case diffs like the e34, regular e36 etc. you need to swap the centers into the e30 case, so the e36 M3 diff is not a direct substitute for the e30.

To increase the amount of lock from 25%, I am pretty sure that you add extra clutches to the LSD, but you would need to look into this further. Metric Mechanic in the states offers you pretty much all the info about different BMW diffs you need. You are using the medium case 188mm...

http://www.metricmechanic.com/pdfs/me ... -differential-booklet.pdf

I have an e30 320i, and am about to swap my diff which is why I have been looking into this stuff.

Good Luck

Luke