What I want to do in nifscope is take the extracted norportcullis which has the behavior I want. It goes up and down when activated.
Then take the mesh shape of the WRDoorCastleSecret which has the shape I want and substitite it for the shape of the portcullis. So I'll have a flat slab that goes up & down when activated.
Then use the texture from WRIntWallSTStr instead of it's origional texture.

It seems as if it should be possible by copying from one nifscape model to the other but I haven't found any tutorials that directly apply or a manual for nifskope.

It can be done but is a bit harder to explain the process quickly --- I don't have time right now to type out the details but try this one - ( http://search.4shared.com/postDownload/EnIUtwIa/norportcullisgate01REdone.html ) -- I copy\pasted the pieces and then also changed the texture path as you indicated - also had to adjust the UVmap a bit (also in Nifskope) so that the texture looked correct (Beth really did not spend any time on the UV on the bottom portion since it was underground on the original and never seen in game so had to adjust it for this use.)

I did not test it in game and it has been awhile since I was using the CK - I believe it should work properly but if not let me know (either here or by PM) and I'll spend some more time on it when I have more time to test. Also if you'd like me to explain the process let me know and I'll type a guide out for you.

It works great. Thank you. A guide would be nice. It would make a great tutorial for those of us who haven't been able to figure out Nifskope.