I got it all together and working correctly. The piece of information I was missing was that I had to bleed the air from the shock. It's described in the Datsun service manual (can anyone point to a download of this?.. all the links I've found are broken). A Nissan parts guy read it to me over the phone.

To bleed the shock, after the oil is put in and every assembled, pull the rod out fully with the shock vertical and the axle at the bottom. Then turn the shock upside down and push the rod fully in. Repeat this several times until the resistance on the rod feels consistant.

I also found that when making long continuous pulls or pushed on the shock, there was little resistance. But if you make several quick and short push pulls, the stiffness appears.

And... for general info. Tokico shocks take 265cc of oil, Atsugi take 280cc. And the gland nut torque is 57-79.5 ft-lbs... so I wouldn't say the torque on the gland nut is all that critical.