Well I've been cleaning up the SE/30 today and it is looking good. The drive mechanism was ceased but I have loosened it off with some WD40. I used steel wool to remove the majority of rust but I will also follow equill's suggestion of using a rust converter to finish the job.

The motherboard on this Mac is pristine and has no capacitor leakage at all. As already mentioned, my other SE/30 has leaking capacitors and has almost lost its sound, so this new one may become the favourite. I haven't yet tested the ethernet card but it will be undoubtedly very useful!

I'll try to get some "finished article" pictures up later today.