what mounts are these ?
The right mount for ALL small blocks is the SAME. ONLY THE LEFT ONE IS DIFFERENT for this vintage of mount (67 - 72). There is about a 1/2 inch difference between the spread for the "ears" for the 273/318 mount compared to the 340/360 mount.
I just went out and measured a 360 block and it is 2 1/2" from ear to ear, a 318 block is 3" between the ears where the bolts go from the block to the mount.
Just measure the spread between the ears where the bolts attach the bracket to the ears on the block. 340/360 left side mounts should measure 2 1/2" and 273/318 mounts will be 3".