Have a very old Norwalk mortise lock with pin tumbler cylinders that takes an unusual shaped key--it has two 90 degree bends in the middle--like an H with the opposite top and bottom legs removed. From what I can determine, this is equivalent to the Keil 128, Ilco 1018 blank, which are long obsolete. Does anyone have an approximate date when Norwalk was using this keyway?

Thanks,
YALE7750