I was getting same response "Error on SCSIRead(), # 5" trying to setup my
macIIx. I found my problem to be during partitioning process. I'm using 
diskforce utility but the other disk utils should have the same options. I had
to initialize the disk with a/ux option first, then go into partition and
define your a/ux. I haven't tried including a MacOS partition yet. This seems
to solve one of the other problems I was seeing during install:

Mounting partition 'A' as /
failed mountfs(), error 22.

Of course, I'm just a beginner to unix so those other fixes I've seen posted
might be quicker and eaiser.

** even with the above messages I was able to boot mac68k and login but I like
the machine to kinda "run clean" so I started over.