CREATE TABLE table_63991 ("Class" CLOB, "Wheel arrangement" CLOB, "Fleet number ( s ) " CLOB, "Manufacturer" CLOB, "Serial numbers" CLOB, "Year made" CLOB, "Quantity made" CLOB, "Quantity preserved" CLOB, "Year ( s )  retired" CLOB)

What are the serial numbers for the locomotives of Class 4-8-4 oooooooo northern?
SELECT "Serial numbers" FROM table_63991 WHERE "Class" = '4-8-4 — oooooooo — northern'
SELECT "Serial numbers" FROM "table_63991" WHERE "Class" = '4-8-4 — oooooooo — northern'