[Bob Bidonde]

The splice joint of the sill would need to be able to withstand bending and twisting. The wood should be the same as the existing sill, and dried to reduce its moisture. Make the splice close to a body mounting bolt aft of the door opening to reduce the vertical bending moment. Consider imbedding metal plates across the top and bottom of the splice.

If the car was mine, I would replace the entire sill without any splicing.