I have a RHD 8/90 build 525i M50 with the 5 speed 5HP18 tranny (Japanese delivery)

I bought it cheap, fixed it up and then the tranny went. I wanted to rebuild it, but my mechanics had a manual and it saved me some money and a lot of time...

However, now the car seems to have a very short final drive ratio, which I don't get as they both have 5 gears...

The motor now does about 3000 rpm at 100kmh (60mph)

I found this resource which shows that they should both be 3.23
http://igge.se/bmw530/final%20drive/final.htm

1. Is the ZF box a serious overdrive or have they installed an e36 box with different ratios? (If this is possible...)

2. I have a 3.45 open diff here or should I get a 3.91?

3. Can one swap the innards of the LSD and use the crown wheels from an open diff? (I know it'd be hard- I am wondering if they will fit/mate at all)

Thank you for reading my queries... Nick