Rodney, your tutorial is so good any one will be able to make a base for any machine. We all strive for perfection but we never make it.
I am also looking for a suitable covering for the tops but never found any I like. I did find some once in automotive upolstry fabric that was thin enough and looked like the old stuff. I have been known to use course canvas and then varnish the heck out of it and it looked really good on the case. You can always paint it in the appropriate color before shellacing or varnishing. Just a thought but it does work.