great project
i wish in some ways i had just gone for a 2.5 m20 (im also a e30zone addict) as i used to love that lump.
dont know if im getting a m30 or m50 in my e30 tourer but i will be up and running soon if i kill myself trying!
keep us updated and lets see some pic's with the split rims on.
oh the 3.91 diff is nice and short so it should suit the skidding nice
should get you about 130 top end