The boss and tapped hole for the upper attachment of the starter brace is on every Chevy block cast since the first one in 1955. The brace is absolutely necessary to support the starter and keep the nose in alignment with the ring gear, along with using the correct knurled starter bolts; many Bubba mechanics leave it off when changing the starter, which results in a short life for the starter and noises that weren't there before.
Photo below is a '67 Corvette, but the arrangement is the same for all Chevy V-8's; the top attachment is a 5/16"-18 x 1/2" bolt, and the stud protruding from the armature housing is 1/4"-20.