I almost hate to ask the obvious, but does something
have specifications
for the SASI protocol? That would go a long way to answering some of
the questions.
Try
http://www.bitsavers.org/pdf/shugart as there are controllers in there.
Also some information in the '1984 Storage Management Products
Handbook' Western Digital. Board WD1002-SMD.
Regards,
Garry