universal joint fitment issue

I have come across that before.
I'm guessing the pinion has a 7290 joint saddle and the Driveshaft has a 7260.
If your 340 has clutch, you will want a proper driveshaft with 7290 joints.
But
I have found that the C-clips on the adapter joint are too thick . I had to transfer the originals from the old 7260,over.
You may be tempted to grind the crosspins shorter, and that may be a viable option; but cutting the same amount of each side will be tricky.

I think there are three different methods of locating those cups in the saddles. There is the type you seem to have; where the C-clips fit between the saddles. And then the type GeorgeH mentions, where the locators are on the saddles. And the third is a U-bolt type with the locators on the U-bolts themselves. I have only seen the first two types in Mopars after 1968.