It will depend on the actual block being used. The early 273 only used 3 bosses on each side of the block for the brackets. Some 318/340/360 block used either 4 on each side (good) or 3, but a different three. If that's the case, you need to cut off an ear off the mount and weld it to where it will bolt to the ear on the block. If you use the 273 brackets on a 340/360, you also need to narrow the bracket on one side, or use washers to take up the difference in width.
