This is the later A+ distributor retainer, which was introduced with the "black box" electronic distributor. If you are using the factory electronic distributor, this is the only clamp that will allow it to fit the block in the correct orientation. This retainer can also be used on points-type distributors, as well as aftermarket distributors. Sold each.
Alternatively, if you have a points-type distributor or aftermarket distributor with a points-type body, then see clamp 613857A. See also FOR049 stainless clamp with graduated markings.
For used/refurbished version, see TAM1671-USED.