Correct rag joint for

[mattfranklin]

I have a 1970 C10 with manual steering.
I'm trying to stay as stock as I can, with AC Delco parts and so on.
My steering box was loose I got a new rebuilt one by AC Delco from Rock Auto. I ordered and installed this:
"ACDELCO 36G0013 {#19321268} Reman; Professional||Remanufactured Manual Gear"

Rock Auto says this box fits from my year up to an '86 C10.

My original box had a slightly smaller shaft with a flat spot.
The new one is a 36-spline with no flat spot and a 0.720" diameter.

My old rag joint will not work.

What is the correct rag joint? I'd prefer a GM-branded part, but I realize that AC Delco is not quite what it was and actually Dorman is probably ok, too.

I was looking at a Dorman 31011, but their inner spline is missing for about a third of the circle. Not exactly a flat, but just a spot without splines cut. Is that what I need?

What is the correct part for this? When I start searching for stock they don't give me spline counts or diameters and I know my original stock rag joint is now "wrong.". When I search on spline counts and diameters all I find is Borgerson or Speedway custom u-joints that sure don't look stock.