If it is horizontal or vertical wood planking, there aren't any values for this. If it is diagonal wood planking, there are some values in the codes of that time. There were studies utilizing nail spacing and capacities for multiple couples - but these were not in any code. In your case the interior sheetrock or plaster or exterior stucco may provide some shear values - but these have been downrated since the 60's. On the other hand, plywood panels were alive and well and these values are available in the Uniform Building Code's of that time. Are there diagonal let-ins in the wallS? I can't remember what people assign a shear value for these configurations - want to say 1000 lbs but you should check. By the way, you cannot add the capacity of sheet rock or stucco to any wood shear element. Either then or today.