Everyone, the good folks over at the Historic Naval Ships Association have posted
"Submarine Attack Course Finder Mark 1 Model 3 Manual, O.D. 453", so we no longer have to guess how the heck to use the Is-Was! In addition, this manual has some fairly clear images of the back side of the Is-Was, so I might eventually be able to complete what I've already put together - but I probably won't be able to get to it for a while, so anyone else can feel free to step up and create the back side of this thing.