Merry Christmas, firstly if only one wheel turns it's not a limited slip [very rare option in those days]. Secondly you are overlooking the differetial gears themselves, those are the gears that allow the two axles to turn at different speeds when you go around a corner. If when doing your test only one wheel turned, you can basically double your driveshafts number of turns giving you a ratio of 4 to 1, hope this helps.