340 cracked pushrods

I was in the process of installing the oil pump shaft in the 69 340. After I got it in I was turning the crank when I heard a "snap". I searched and found a split pushrod(no. one intake).There are others that look like they are starting to split.These are the ones that came on this engine.The cam is mopar no. p4452782, the new springs (recommended for this cam) are mopar no. P4120249. Lifters are same length as the originals. I cleaned and inspected these before the installation and found no damage.Could I have the wrong combination or weak pushrods ?