Power Steering & Steering Coupling issue, need some Help?

[longhorn70gmc]

Hey all,
I have a predicament. I have removed the Power Steering Box off of my 1970 ¾ GMC Longhorn. I have removed the Steering Coupling Assembly that attaches the Steering Column to the Power Steering Box. I have ordered and received two new Power Steering Boxes and both Splines measure out at 7/8.
The Original Steering Coupling Assembly measures out at ¾ of an inch and the new one I purchased measures out at ¾ of an inch as well. The new Steering Coupling Assembly is for 1969-1986 GM.
On the old Power Steering Box the spline measures out at ¾ of an inch and the old and new Steering Coupling Assembly slides on the old Power Steering Box no problem, but it will not go on the new ones.
To sum it up; I have ordered two new Power Steering Boxes and one Steering Coupling Assembly and have gotten together with a trusted local Auto Zone Representative and am just coming up short on getting solution for this replacement and install.
My question to you all is what else can I do here or try to fix this situation? Another question is do I have to have the new Steering Coupling pressed on? Please any and all assistance appreciated?
R/
Billy
Note: I am currently unable to post this thread in Suspension and Steering Section, so I apologize for not following protocol rules for posting threads and the intended titled sections.