Prototrak encoder info needed

I was the recipient of a bit of good luck and timing, finding a post on
another list
I subscribe to offering a Prototrak control almost complete for $100 in
the SF bay area less than a day before I was going down. I'm back, with
the control sitting on the floor. It appears everything is here but the
encoders. Fellow that scrounged this saw two cables coming out of each
motor and assumed they were power/encoder. Motors must use a tach, as
early ProtoTraks used TravDials fitted with rotary encoders for
position. He didn't pick the encoders out of the pile because he didn't
realize they were part of the setup.
So, I really don't think I want to buy new encoders, and I am not yet
sure SWI is going to be willing to provide the info. Does anyone have an
older ProtoTrak setup? If so, are there any specs anywhere in your docs
giving the encoder count and any details on what type of signal the
encoders output?
I suspect I will run across a set of these on eBay sooner or later, but
if I can possibly cobble up an interface to use linear scales, that
would be cool.

Jon A.