measuring and installing ujoint

[Sick5]

Ran into a rear end that its Yoke is smooth. It doesn't have the small stoppers at the end to keep the ujoint from moving. I'm not sure what year it is. But i do know it had leaf spring and its a 10 bolt 8.5.
going from 63 6 lug to this 5 lug rear end. how do i measure the yoke to get the correct ujoint with this style of yoke?

I've measured the out side diameter of the yoke but i only find close to that measurement. im not sure but i think on this i need to measure the inside half circle to get the size of the ujoint (inside clips) im assuming.