A lug nut on the threads will give you something to hold on to for spinning.  Same pitch and size.

The spindle pin is designed to be tensioned against the bushings to make it all one piece. The serrations on the end of the stock bushings help to accomplish this. I believe the poly bushing have an inner sleeve that tries to duplicate the same thing. I also believe that is why the spindle pin seems t o be so soft and easily damaged by beating on it. As long as the spindle pin doesn't rock in the bore then I would think it should be fine. I worked on mine until I could push them in by hand. I wouldn't want them any tighter than I could tap them in with a rubber mallet. They were snug but not tight and fairly easy to rotate in place.

You should be able to insert the spindle pin all the way and spin it 360 degrees with just two fingers. If you can't do that, then I suspect there's a burr inside that's causing an interference fit. There should be no tools required to get that pin properly into place.

Success...a "rat" file, some light lube and about 30 minutes of work and now the spindle pin passes right through by hand.  And I think it was a combination of left over corrosion and at least a couple small burrs because a close inspection of the spindle pin after initially tapping it through with a rubber hammer did reveal a couple light scorch marks along its horizontal axis.  But I couldn't see anything visually when looking through the hole with a light.

Anyway...all is good now with this problem.  On to the next...and thanks for all the good advice!

Excellent. Keep coming to us with the easy issues. We like those.

Don't forget to use copious amounts of anti-corrosion anti-seize on your new spindle pins when you slide them in for the final installation.

And if you didn't already know.... The location of the notch for the lock pin is not in the center of the spindle pin. It's offset a little bit. (The pin is not symmetric). There is a correct front and back.

Point is... If you haven't already done so, it's a lot easier to determine which is the correct installation direction when the parts are off the car and not all slathered with copious amounts of lube. Mark it with a sharpie or something now while everything is clean so you don't have to futz with it while it's all slippy.