To be precise, '64-'65 (#315) heads, and, '66 (#178) heads are small chamber, 5/16" attaching bolts with the weird angle...'67 (#920) heads are small chamber, 3/8" bolts with conventional angle. The '68-'69 (#675) heads had the large chambers and non-adjustable, hydraulic rocker arms. These heads (#675) also cont'd on through '74 on 318's.
