It used to be that an annular throwout bearing was made by Tilton and found in Trans Am cars. Now they're called Concentric Slave Cylinders and standard fare on Mustangs--and have been for a while. For '13 only a minor change to the TO bearing's retainer clip was needed, and the new TO assembly serves as the new service part for '10-and-later GT500s. What's truly new in this '13 GT500 bellhousing is the inverted V of oil passages cast into the bulkhead shared by the bellhousing and front of transmission. The passages converge at the transmission oil pump, with the passage at right forming the pump pickup, and the passage at left connecting to the cooler lines on cars with the optional Track Cooling package.