Which Universal Joint do I need?

[D-n-Tyke]

I swapped out the original rear end in my 1969 C20 Suburban for a rear end out of a 1971 C10 so I could have a 5 lug set up. I thought I had read before doing this that both the C10 and the C20 used the same u-joint at the differential. When I looked at what I have tonight, the u-joint cups on the C20 driveshaft and larger in diameter than the bores in the differential yoke. What u-joint do I need to get to make this setup work?

1969 C20 Suburban 396/TH400, with 2-piece shaft
1971 C10 donor rear end. Motor/trans combo unknown.