Steering gear - Spline Count & OD

[jwbchevy502]

I am in the process of adding a new tilt wheel to my truck and can't determine if the steering box is a 13/16"-36 spline or a 3/4" - 30 spline shaft. I know that the 13/16" were used up until around 1976 and then 3/4" from 1977-1986. The only info I have is that the casting number on the box is a GM 7802644 which appears to be a Saginaw box newer generation which would indicate. I purchased a conversion kit from manual to power a few years back and can't find the info in any of the documentation I have. I am in the process of adding a tilt wheel column and need to determine what shaft/spline setup required so I can purchase the correct coupler to mate up to my new tilt wheel. Any help in verifying the correct spline / shaft OD would be apprciated. Thanks