Thanks for the advice on my rear differential questions. Just to update y'all, I was able to score a 72 C10 rear end. Literally the only one I've seen for sale. It has a 307 gear ratio, but is an open carrier. So, not exactly what I wanted, but close enough. I can always add the LTD slip later.
That being said. The install opened up a whole new set of issues. U-joint, pinion yoke issues, wheel cylinders didn't fit, parking brake differences, etc. The damn trailing arm split right in two. We welded the trailing arm back together and are working through the other issues. So, It's all good. I have the front suspension to install next. It's all back from powder coat and I had the machine shop install new lower ball joints and a-arm bushings. Lots to do!
Thanks again for all your help.
Bill