Help with brake wheel cylinder

[jj72c10]

I have a question regarding replacement wheel cylinders for the rear brakes. I have a 72 C10 half ton I am redoing. I just finished putting a new Eaton posi in the rear and was replacing all the brake components as well. I went to replace the wheel cylinders and none of them would fit. I went to O'Riellys, AutoZone, Advanced Auto and CarQuest. Everyone any of them had was different then the originals I took off. They were too wide and would not fit between the ears on the backing plate. The rearend is the original in the truck, I was able to verify that. The factory number on the original cylinders cross-referenced to the new bigger castings. What I did find out is that the rebuild kits for the 6 cylinder trucks which mine was originally matched what I took off. If I wanted a complete new wheel cylinder, they were bigger. Has anyone ran into this problem? I bought the rebuild kits and honed my originals out but would rather buy new. Help!

Thanks,

JJ