Trouble Installing 18 spline A-833 through dual disc clutch assy.

So you are saying that when the engine was on the floor, you successfully installed the trans all the way? Had my engine out of my '69 a few weeks back, trans stayed in car. Done this several times, but could not get the engine back in place. Alignment tool went in just fine. Pulled the engine back out for the 3rd time, borrowed a spare trans from my friend, it wouldn't go in on the floor. So apart for the 3rd time. From trying to install by my self, I had the angle off, though I had looked at it umpteen times. The input shaft had boogered the splines from incorrect angle. Took a 3 sided file and corrected the leading edge of the splines as good as I could, trans went right in.