Done!

Thank you all for your help. I still had the problem, that Apple SC HD 2.0.3 did initialize but never finished verifying the disk, but a patched version of SCHD 7.3.5 finally did it. I'm now a proud owner of a SE 1/40 with a 500MB Quantum HDD. So this machine should be called SE 1/500. }

Cheers,

Blackswan