There are two patterns of shock link that may be appropriate to your truck. The ones Bob is referring to (with rubber discs and large washers on either side of the axle mount) may be referred to as pear type. There is also a model that has similar tapered stud mounts at both top and bottom. These are available "off the shelf" from Vintage Power Wagons in length that suits Chev CMP. This type does require a small adapter bracket to convert the crosswise taper similar to the top of the link to the lengthwise thread similar to the spear type.
Bob has the spear type on his C15A, I have the link with 2 studs. Perhaps while Bob is taking photos and measurements, he can also check mine to let you see both types together. The length you will need is the center-to-center distance on the pins. I'm quite sure the link I used (without needing to modify) was "NOS Late Shock Absorber Link" on page 70 of
http://www.vintagepowerwagons.com/pd.../16springs.pdf with the length given as 9-1/4"