These closed chamber (or quench) style heads are found on the 1970/71 M-code 351C-4V. The heads feature huge ports, 61.3-64.3cc combustion chambers, 2.198" intake valves and 1.715" exhaust valves. These engines are designed for hydraulic lifter camshafts and use slotted rocker arm pedestals, for non-adjustable rockers. These slots maintain the angle of the rocker arm and the pushrod alignment. These heads can be modified to fit a 289 or 302 block for a homemade Boss. The square water outlets in the upper corners of the deck face must be plugged. This can be accomplished by drilling and tapping the casting for a pipe plug. A new water outlet on the intake manifold face must be drilled.