74 Duster, resto mod 6.4 front end rebuild questions

I believe you are on the right track, I would say you have the wrong coupler.

As I remember (????) you did not know what spline or shaft size you had but told me you were using a PST manual steering box, so I believe I got the shaft spline and count from the PST site?

let me know what PST says. Are you sure you have a PST steering box?
I hope so as thats what i purchased it as lol, i have contacted Kanter auto who now own or merged with PST, to find out the spline size. I can also see if the standard coupler fits it once i pull the saft out. If it does then its 3/4. Either way mate the pipes now fit with clearance. If i have to buy a 3/4 so be it as happ as knowing i dont have to rebuild pipes haha