Randy, the J spring might have changed a little, but since your replacement forend does have the rectangular release, then you can be sure it was made in 1939 or later.
Drew is right about the cost, in a 1939 catalog, standard two trigger Ideal Grade was $60.25, so a set of extra barrels were $30.00. Two trigger Specialty Grade was $100.00, extra set of barrels $50.00. In a 1948 Repair Catalog for the L.C. Smith Gun Co. a set of extra barrels were $64.50 and a Specialty was $100.00. Forend wood fitted, $10.50 and $15.50.
