The standard Mopar U joints sizes are the 7260 and the little larger 7290, I'm not sure of the name or number of the U joint Mopar started using with the Dana 60 rear ends in the H.D. 4 speed cars in either 1966 or 1967, I'm thinking it is a 1330, maybe not
I think of how strong the U joint pins that the cups and needle bearing ride on by their diameter and length, the 7260 is around 3/8 to 1/2 shorter overall than the 7290 are, the longer the length on those pins the more mechanical advantage the breaking force has to break them, me thinks narrower U joints and the end of the pins being closer to the closer to the center of the pinion gear is stronger