This bellhousing is modeled after the famous "621" and designed to bolt to Gen III LS-engines. This bellhousing, along with a 168 tooth flywheel and 11" clutch, allows the use of an original 4-speed Saginaw, Muncie, or Borg-Warner transmission, including the original clutch linkage and starter. Made from CNC machined heavy cast aluminum, heat-treated and reinforced with extensive thick webbing, this is one of the strongest cast aluminum bellhousings available. Depth/ thickness mounting surface to mounting surface is 6 3/8" Clears 168 tooth 14" Flywheels with factory 11" clutch discs. Works with GM transmissions with a 4.675" O.D. Bearing Retainer. 1/2"-13 tapped hole for z-bar manual clutch linkage, if needed.