steering box-rag joint cofirmation

[dragon65]

So I have read all the steering info on here over and over again.
Please confirm my thoughts before I slap down another $50 on a rag joint.
I have just purchased a Cardone 27-7501 steering box- its a saginaw 7802644. I need to confirm the rag joint should be a Dorman-31015....which is 13/16 and the splines are 36 even though there is the flat spot on the input shaft. From my education here if the flat spot was not there there would be 36.....in my case the flat spot is there and I count 31.....hence I need to order the Dorman 31015 rag joint and then a rag joint coupler to mate to the steering shaft.
Please can someone confirm my info.......If there is a comparable rag joint to the Dorman I am not opposed to a recommendation as long as I have the part number and the cost is lower

I am converting manual on a 65 gmc 6cyl.....swb to power.

Thank you soooo much for any input