You can use any cluster with the M42, if you have the four-cylinder coding chip. I think they're still available from BMW...
I'm pretty sure I have one working M20B25 gauge cluster (with 6500rpm redline tach) if you're interested. I have a bunch of eta clusters too, but they won't work for you.
I might have a C101 body side plug too, let me check & I'll get back to you tomorrow.