Do either of you two guys read Amazing Computing? Vol 1 #6, page 73
has an article by Thom Sterling on the Amiga disk controller (in fact, it's
titled "Fun with the Amiga disk controller"). As a real amachoor, I don't
understand nearly as much of the article as I would like to, but it details
the differences between MFM,and a different conversion scheme he leaves
unnamed, but which I presume is the RLL you mention (he does, however refer
to it as a "7/12" method, if that helps). Just thought I'd mention it.