If you are planning a T5 swap using the new bellhousing, or have one and don't
have the boot yet,
then here is your P/N; Ford Service Part # D9HZ-7513-A
It's called a "Shield Assembly"---piece o' rubber.
It's not as good as the old boots, but it is a heck of a lot better than having that open hole around the clutch arm. ---Courtesy of 66fastback