74 Duster, resto mod 6.4 front end rebuild questions

I couldn't get the photos to load in messages, so the bourgeon coupler is just ever so slightly smaller than the coupler that fits the PST steering box. Looks to be just over 1.5mm difference not sure what that is in inches lol. Do you think i have the wrong coupler or a machining issue?

Edit just looked a 11/16th is 17.5mm and 19mm is 3/4 so that would make sense to why. (I think the standard manual mopars are 3/4 as well) I have contacted PST to see if they can confirm the spline size
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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?