Just when I thought I was done

I can't beleive that I am saying this but just as I am so close to being finished with this project I am getting ready to take it all back apart.  In the picture below you can see the spline shaft and the spline coupling.  This picture is after I had taken it apart and before I went in to bed that night. I took a picture so that I could remember how it all had been.  I didn't want to forget so I simply laid the coupling in place but did not put it on in the position that it was orgionaly.  It was very difficult to take off and I did not want to have to heat it up and knock it off again. 

When I put the tractor back together I put installed the coupling to a small line on the spline shaft where it looked like it was before.  But when I was assembling the transmission to the rear end I almost had it completely mated together before it engaged into the spline fit. 

As I think about it I think it would be best to check to see how long of an engagement it has before I start using this tractor as a bulldozer pounding the dirt and snow.  I don't want the spline in the rear end or the coupling to strip off.  I hope to do it all in one day before it snows on me.