I am faced with the same construction at my house, does anyone have any input?

Caution should be taken before attempting this type of work when removal of a structural element of the building is involved. Especially since this building was constructed in 1920.

Back then there was virtually no building code and/or inspections to regulate how a house was built. Therefore there are many different types of construction and many were built by the home owner not a contractor.

The most common type of construction back then was the balloon frame. Without plywood they used diagonal or shiplap boards to give the walls lateral stability.

The only way to be sure would be to have a structural engineer or qualified general contractor to examine the building first. The plywood would work but the main concern is how much of the shiplap sheathing you can remove at one time before replacing it with plywood.

Glenn